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2.JS 基础知识点及常考面试题（一）.htm
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data-v-40eb6fce="">购买小册时自动使用专享券</div><div class="btn-success-footer" data-v-40eb6fce=""><div class="btn-ok" data-v-40eb6fce="">知道了</div><div class="btn-ok btn-link" data-v-40eb6fce="">前往小册首页</div></div></div><div class="model fail" style="display:none;" data-v-40eb6fce=""><div class="heading" data-v-40eb6fce="">领取失败</div><div class="content-text" data-v-40eb6fce="">本活动仅适用于小册新用户</div><div class="btn-ok" data-v-40eb6fce="">知道了</div></div></div><!----></div><!----><div data-v-25b273c2="" data-v-c5c2a81e="" class="book-read-view"><section data-v-25b273c2="" class="book-section"><div data-v-25b273c2="" class="book-summary"><div data-v-25b273c2="" class="book-summary-masker"></div><div data-v-25b273c2="" class="book-summary-inner"><div data-v-25b273c2="" class="book-summary__header"><a data-v-25b273c2="" href="https://juejin.im/books" target="" rel="" class="logo"><img data-v-25b273c2="" src="./2.JS 基础知识点及常考面试题（一）_files/logo.a7995ad.svg"></a><div data-v-25b273c2="" class="label">小册</div><!----></div><!----><div data-v-d0eb2184="" data-v-25b273c2="" class="book-directory book-directory bought"><a data-v-d0eb2184="" class="section section-link read"><div data-v-d0eb2184="" class="step"><div data-v-d0eb2184="" class="step-btn">1</div></div><div data-v-d0eb2184="" class="center"><div data-v-d0eb2184="" class="title">小册食用指南</div><!----><!----></div><!----></a><a data-v-d0eb2184="" class="section route-active section-link"><div data-v-d0eb2184="" class="step"><div data-v-d0eb2184="" class="step-btn">2</div></div><div data-v-d0eb2184="" class="center"><div data-v-d0eb2184="" class="title">JS 基础知识点及常考面试题（一）</div><!----><!----></div><!----></a><a data-v-d0eb2184="" class="section section-link"><div data-v-d0eb2184="" class="step"><div data-v-d0eb2184="" class="step-btn">3</div></div><div data-v-d0eb2184="" class="center"><div data-v-d0eb2184="" class="title">JS 基础知识点及常考面试题（二）</div><!----><!----></div><!----></a><a data-v-d0eb2184="" class="section section-link"><div data-v-d0eb2184="" class="step"><div data-v-d0eb2184="" class="step-btn">4</div></div><div data-v-d0eb2184="" class="center"><div data-v-d0eb2184="" class="title">ES6 知识点及常考面试题</div><!----><!----></div><!----></a><a data-v-d0eb2184="" class="section section-link"><div data-v-d0eb2184="" class="step"><div data-v-d0eb2184="" class="step-btn">5</div></div><div data-v-d0eb2184="" class="center"><div data-v-d0eb2184="" class="title">JS 异步编程及常考面试题</div><!----><!----></div><!----></a><a data-v-d0eb2184="" class="section section-link"><div data-v-d0eb2184="" class="step"><div data-v-d0eb2184="" class="step-btn">6</div></div><div data-v-d0eb2184="" class="center"><div data-v-d0eb2184="" class="title">手写 Promise</div><!----><!----></div><!----></a><a data-v-d0eb2184="" class="section section-link"><div data-v-d0eb2184="" class="step"><div data-v-d0eb2184="" class="step-btn">7</div></div><div data-v-d0eb2184="" class="center"><div data-v-d0eb2184="" class="title">Event Loop</div><!----><!----></div><!----></a><a data-v-d0eb2184="" class="section section-link"><div data-v-d0eb2184="" class="step"><div data-v-d0eb2184="" class="step-btn">8</div></div><div data-v-d0eb2184="" class="center"><div data-v-d0eb2184="" class="title">JS 进阶知识点及常考面试题</div><!----><!----></div><!----></a><a data-v-d0eb2184="" class="section section-link"><div data-v-d0eb2184="" class="step"><div data-v-d0eb2184="" class="step-btn">9</div></div><div data-v-d0eb2184="" class="center"><div data-v-d0eb2184="" class="title">JS 思考题</div><!----><!----></div><!----></a><a data-v-d0eb2184="" class="section section-link"><div data-v-d0eb2184="" class="step"><div data-v-d0eb2184="" class="step-btn">10</div></div><div data-v-d0eb2184="" class="center"><div data-v-d0eb2184="" class="title">DevTools Tips</div><!----><!----></div><!----></a><a data-v-d0eb2184="" class="section section-link"><div data-v-d0eb2184="" class="step"><div data-v-d0eb2184="" class="step-btn">11</div></div><div data-v-d0eb2184="" class="center"><div data-v-d0eb2184="" class="title">浏览器基础知识点及常考面试题</div><!----><!----></div><!----></a><a data-v-d0eb2184="" class="section section-link"><div data-v-d0eb2184="" class="step"><div data-v-d0eb2184="" class="step-btn">12</div></div><div data-v-d0eb2184="" class="center"><div data-v-d0eb2184="" class="title">浏览器缓存机制</div><!----><!----></div><!----></a><a data-v-d0eb2184="" class="section section-link"><div data-v-d0eb2184="" class="step"><div data-v-d0eb2184="" class="step-btn">13</div></div><div data-v-d0eb2184="" class="center"><div data-v-d0eb2184="" class="title">浏览器渲染原理</div><!----><!----></div><!----></a><a data-v-d0eb2184="" class="section section-link"><div data-v-d0eb2184="" class="step"><div data-v-d0eb2184="" class="step-btn">14</div></div><div data-v-d0eb2184="" class="center"><div data-v-d0eb2184="" class="title">安全防范知识点</div><!----><!----></div><!----></a><a data-v-d0eb2184="" class="section section-link"><div data-v-d0eb2184="" class="step"><div data-v-d0eb2184="" class="step-btn">15</div></div><div data-v-d0eb2184="" class="center"><div data-v-d0eb2184="" class="title">从 V8 中看 JS 性能优化</div><!----><!----></div><!----></a><a data-v-d0eb2184="" class="section section-link"><div data-v-d0eb2184="" class="step"><div data-v-d0eb2184="" class="step-btn">16</div></div><div data-v-d0eb2184="" class="center"><div data-v-d0eb2184="" class="title">性能优化琐碎事</div><!----><!----></div><!----></a><a data-v-d0eb2184="" class="section section-link"><div data-v-d0eb2184="" class="step"><div data-v-d0eb2184="" class="step-btn">17</div></div><div data-v-d0eb2184="" class="center"><div data-v-d0eb2184="" class="title">Webpack 性能优化</div><!----><!----></div><!----></a><a data-v-d0eb2184="" class="section section-link"><div data-v-d0eb2184="" class="step"><div data-v-d0eb2184="" class="step-btn">18</div></div><div data-v-d0eb2184="" class="center"><div data-v-d0eb2184="" class="title">实现小型打包工具</div><!----><!----></div><!----></a><a data-v-d0eb2184="" class="section section-link"><div data-v-d0eb2184="" class="step"><div data-v-d0eb2184="" class="step-btn">19</div></div><div data-v-d0eb2184="" class="center"><div data-v-d0eb2184="" class="title">React 和 Vue 两大框架之间的相爱相杀</div><!----><!----></div><!----></a><a data-v-d0eb2184="" class="section section-link"><div data-v-d0eb2184="" class="step"><div data-v-d0eb2184="" class="step-btn">20</div></div><div data-v-d0eb2184="" class="center"><div data-v-d0eb2184="" class="title">Vue 常考基础知识点</div><!----><!----></div><!----></a><a data-v-d0eb2184="" class="section section-link"><div data-v-d0eb2184="" class="step"><div data-v-d0eb2184="" class="step-btn">21</div></div><div data-v-d0eb2184="" class="center"><div data-v-d0eb2184="" class="title">Vue 常考进阶知识点</div><!----><!----></div><!----></a><a data-v-d0eb2184="" class="section section-link"><div data-v-d0eb2184="" class="step"><div data-v-d0eb2184="" class="step-btn">22</div></div><div data-v-d0eb2184="" class="center"><div data-v-d0eb2184="" class="title">React 常用知识点</div><!----><div data-v-d0eb2184="" class="sub-line"><div data-v-d0eb2184="" class="writing">写作中...</div></div></div><!----></a><a data-v-d0eb2184="" class="section section-link"><div data-v-d0eb2184="" class="step"><div data-v-d0eb2184="" class="step-btn">23</div></div><div data-v-d0eb2184="" class="center"><div data-v-d0eb2184="" class="title">React 进阶</div><!----><div data-v-d0eb2184="" class="sub-line"><div data-v-d0eb2184="" class="writing">写作中...</div></div></div><!----></a><a data-v-d0eb2184="" class="section section-link"><div data-v-d0eb2184="" class="step"><div data-v-d0eb2184="" class="step-btn">24</div></div><div data-v-d0eb2184="" class="center"><div data-v-d0eb2184="" class="title">监控</div><!----><div data-v-d0eb2184="" class="sub-line"><div data-v-d0eb2184="" class="writing">写作中...</div></div></div><!----></a><a data-v-d0eb2184="" class="section section-link"><div data-v-d0eb2184="" class="step"><div data-v-d0eb2184="" class="step-btn">25</div></div><div data-v-d0eb2184="" class="center"><div data-v-d0eb2184="" class="title">TCP / UDP</div><!----><div data-v-d0eb2184="" class="sub-line"><div data-v-d0eb2184="" class="writing">写作中...</div></div></div><!----></a><a data-v-d0eb2184="" class="section section-link"><div data-v-d0eb2184="" class="step"><div data-v-d0eb2184="" class="step-btn">26</div></div><div data-v-d0eb2184="" class="center"><div data-v-d0eb2184="" class="title">HTTP 及 TLS</div><!----><div data-v-d0eb2184="" class="sub-line"><div data-v-d0eb2184="" class="writing">写作中...</div></div></div><!----></a><a data-v-d0eb2184="" class="section section-link"><div data-v-d0eb2184="" class="step"><div data-v-d0eb2184="" class="step-btn">27</div></div><div data-v-d0eb2184="" class="center"><div data-v-d0eb2184="" class="title">HTTP 2.0</div><!----><div data-v-d0eb2184="" class="sub-line"><div data-v-d0eb2184="" class="writing">写作中...</div></div></div><!----></a><a data-v-d0eb2184="" class="section section-link"><div data-v-d0eb2184="" class="step"><div data-v-d0eb2184="" class="step-btn">28</div></div><div data-v-d0eb2184="" class="center"><div data-v-d0eb2184="" class="title">输入 URL 到页面渲染的整个流程</div><!----><div data-v-d0eb2184="" class="sub-line"><div data-v-d0eb2184="" class="writing">写作中...</div></div></div><!----></a><a data-v-d0eb2184="" class="section section-link"><div data-v-d0eb2184="" class="step"><div data-v-d0eb2184="" class="step-btn">29</div></div><div data-v-d0eb2184="" class="center"><div data-v-d0eb2184="" class="title">设计模式</div><!----><div data-v-d0eb2184="" class="sub-line"><div data-v-d0eb2184="" class="writing">写作中...</div></div></div><!----></a><a data-v-d0eb2184="" class="section section-link"><div data-v-d0eb2184="" class="step"><div data-v-d0eb2184="" class="step-btn">30</div></div><div data-v-d0eb2184="" class="center"><div data-v-d0eb2184="" class="title">常见数据结构</div><!----><div data-v-d0eb2184="" class="sub-line"><div data-v-d0eb2184="" class="writing">写作中...</div></div></div><!----></a><a data-v-d0eb2184="" class="section section-link"><div data-v-d0eb2184="" class="step"><div data-v-d0eb2184="" class="step-btn">31</div></div><div data-v-d0eb2184="" class="center"><div data-v-d0eb2184="" class="title">常考算法题解析</div><!----><div data-v-d0eb2184="" class="sub-line"><div data-v-d0eb2184="" class="writing">写作中...</div></div></div><!----></a><a data-v-d0eb2184="" class="section section-link"><div data-v-d0eb2184="" class="step"><div data-v-d0eb2184="" class="step-btn">32</div></div><div data-v-d0eb2184="" class="center"><div data-v-d0eb2184="" class="title">CSS 常考面试题解析</div><!----><div data-v-d0eb2184="" class="sub-line"><div data-v-d0eb2184="" class="writing">写作中...</div></div></div><!----></a><a data-v-d0eb2184="" class="section section-link"><div data-v-d0eb2184="" class="step"><div data-v-d0eb2184="" class="step-btn">33</div></div><div data-v-d0eb2184="" class="center"><div data-v-d0eb2184="" 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<p>JS 对于每位前端开发都是必备技能，在小册中我们也会有多个章节去讲述这部分的知识。首先我们先来熟悉下 JS 的一些常考和容易混乱的基础知识点。</p>
<h2 class="heading" data-id="heading-1">原始（Primitive）类型</h2>
<blockquote class="warning"><p>涉及面试题：原始类型有哪几种？null 是对象嘛？
</p></blockquote><p>在 JS 中，存在着 6 种原始值，分别是：</p>
<ul>
<li><code>boolean</code></li>
<li><code>null</code></li>
<li><code>undefined</code></li>
<li><code>number</code></li>
<li><code>string</code></li>
<li><code>symbol</code></li>
</ul>
<p>首先原始类型存储的都是值，是没有函数可以调用的，比如 <code>undefined.toString()</code></p>
<p></p><figure><img class="lazyload inited" data-src="https://user-gold-cdn.xitu.io/2018/11/14/16711c4f991c73ac?imageView2/0/w/1280/h/960/format/webp/ignore-error/1" data-width="526" data-height="53" src="data:image/svg+xml;utf8,<?xml version="1.0"?><svg xmlns="http://www.w3.org/2000/svg" version="1.1" width="526" height="53"></svg>"><figcaption></figcaption></figure><p></p>
<p>此时你肯定会有疑问，这不对呀，明明 <code>'1'.toString()</code> 是可以使用的。其实在这种情况下，<code>'1'</code> 已经不是原始类型了，而是被强制转换成了 <code>String</code> 类型也就是对象类型，所以可以调用 <code>toString</code> 函数。</p>
<p>除了会在必要的情况下强转类型以外，原始类型还有一些坑。</p>
<p>其中 JS 的 <code>number</code> 类型是浮点类型的，在使用中会遇到某些 Bug，比如 <code>0.1 + 0.2 !== 0.3</code>，但是这一块的内容会在进阶部分讲到。<code>string</code> 类型是不可变的，无论你在 <code>string</code> 类型上调用何种方法，都不会对值有改变。</p>
<p>另外对于 <code>null</code> 来说，很多人会认为他是个对象类型，其实这是错误的。虽然 <code>typeof null</code> 会输出 <code>object</code>，但是这只是 JS 存在的一个悠久 Bug。在 JS 的最初版本中使用的是 32 位系统，为了性能考虑使用低位存储变量的类型信息，<code>000</code> 开头代表是对象，然而 <code>null</code> 表示为全零，所以将它错误的判断为 <code>object</code> 。虽然现在的内部类型判断代码已经改变了，但是对于这个 Bug 却是一直流传下来。</p>
<h2 class="heading" data-id="heading-2">对象（Object）类型</h2>
<blockquote class="warning"><p>涉及面试题：对象类型和原始类型的不同之处？函数参数是对象会发生什么问题？
</p></blockquote><p>在 JS 中，除了原始类型那么其他的都是对象类型了。对象类型和原始类型不同的是，原始类型存储的是值，对象类型存储的是地址（指针）。当你创建了一个对象类型的时候，计算机会在内存中帮我们开辟一个空间来存放值，但是我们需要找到这个空间，这个空间会拥有一个地址（指针）。</p>
<pre><code class="hljs js" lang="js"><span class="hljs-keyword">const</span> a = []
</code></pre><p>对于常量 <code>a</code> 来说，假设内存地址（指针）为 <code>#001</code>，那么在地址 <code>#001</code> 的位置存放了值 <code>[]</code>，常量 <code>a</code> 存放了地址（指针） <code>#001</code>，再看以下代码</p>
<pre><code class="hljs js" lang="js"><span class="hljs-keyword">const</span> a = []
<span class="hljs-keyword">const</span> b = a
b.push(<span class="hljs-number">1</span>)
</code></pre><p>当我们将变量赋值给另外一个变量时，复制的是原本变量的地址（指针），也就是说当前变量 <code>b</code> 存放的地址（指针）也是 <code>#001</code>，当我们进行数据修改的时候，就会修改存放在地址（指针） <code>#001</code> 上的值，也就导致了两个变量的值都发生了改变。</p>
<p>接下来我们来看函数参数是对象的情况</p>
<pre><code class="hljs js" lang="js"><span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">test</span>(<span class="hljs-params">person</span>) </span>{
person.age = <span class="hljs-number">26</span>
person = {
<span class="hljs-attr">name</span>: <span class="hljs-string">'yyy'</span>,
<span class="hljs-attr">age</span>: <span class="hljs-number">30</span>
}
<span class="hljs-keyword">return</span> person
}
<span class="hljs-keyword">const</span> p1 = {
<span class="hljs-attr">name</span>: <span class="hljs-string">'yck'</span>,
<span class="hljs-attr">age</span>: <span class="hljs-number">25</span>
}
<span class="hljs-keyword">const</span> p2 = test(p1)
<span class="hljs-built_in">console</span>.log(p1) <span class="hljs-comment">// -> ?</span>
<span class="hljs-built_in">console</span>.log(p2) <span class="hljs-comment">// -> ?</span>
</code></pre><p>对于以上代码，你是否能正确的写出结果呢？接下来让我为了解析一番：</p>
<ul>
<li>首先，函数传参是传递对象指针的副本</li>
<li>到函数内部修改参数的属性这步，我相信大家都知道，当前 <code>p1</code> 的值也被修改了</li>
<li>但是当我们重新为了 <code>person</code> 分配了一个对象时就出现了分歧，请看下图</li>
</ul>
<p></p><figure><img class="lazyload inited" data-src="https://user-gold-cdn.xitu.io/2018/11/14/16712ce155afef8c?imageView2/0/w/1280/h/960/format/webp/ignore-error/1" data-width="658" data-height="414" src="data:image/svg+xml;utf8,<?xml version="1.0"?><svg xmlns="http://www.w3.org/2000/svg" version="1.1" width="658" height="414"></svg>"><figcaption></figcaption></figure><p></p>
<p>所以最后 <code>person</code> 拥有了一个新的地址（指针），也就和 <code>p1</code> 没有任何关系了，导致了最终两个变量的值是不相同的。</p>
<h2 class="heading" data-id="heading-3">typeof vs instanceof</h2>
<blockquote class="warning"><p>涉及面试题：typeof 是否能正确判断类型？instanceof 能正确判断对象的原理是什么？
</p></blockquote><p><code>typeof</code> 对于原始类型来说，除了 <code>null</code> 都可以显示正确的类型</p>
<pre><code class="hljs js" lang="js"><span class="hljs-keyword">typeof</span> <span class="hljs-number">1</span> <span class="hljs-comment">// 'number'</span>
<span class="hljs-keyword">typeof</span> <span class="hljs-string">'1'</span> <span class="hljs-comment">// 'string'</span>
<span class="hljs-keyword">typeof</span> <span class="hljs-literal">undefined</span> <span class="hljs-comment">// 'undefined'</span>
<span class="hljs-keyword">typeof</span> <span class="hljs-literal">true</span> <span class="hljs-comment">// 'boolean'</span>
<span class="hljs-keyword">typeof</span> <span class="hljs-built_in">Symbol</span>() <span class="hljs-comment">// 'symbol'</span>
</code></pre><p><code>typeof</code> 对于对象来说，除了函数都会显示 <code>object</code>，所以说 <code>typeof</code> 并不能准确判断变量到底是什么类型</p>
<pre><code class="hljs js" lang="js"><span class="hljs-keyword">typeof</span> [] <span class="hljs-comment">// 'object'</span>
<span class="hljs-keyword">typeof</span> {} <span class="hljs-comment">// 'object'</span>
<span class="hljs-keyword">typeof</span> <span class="hljs-built_in">console</span>.log <span class="hljs-comment">// 'function'</span>
</code></pre><p>如果我们想判断一个对象的正确类型，这时候可以考虑使用 <code>instanceof</code>，因为内部机制是通过原型链来判断的，在后面的章节中我们也会自己去实现一个 <code>instanceof</code>。</p>
<pre><code class="hljs js" lang="js"><span class="hljs-keyword">const</span> Person = <span class="hljs-function"><span class="hljs-keyword">function</span>(<span class="hljs-params"></span>) </span>{}
<span class="hljs-keyword">const</span> p1 = <span class="hljs-keyword">new</span> Person()
p1 <span class="hljs-keyword">instanceof</span> Person <span class="hljs-comment">// true</span>
<span class="hljs-keyword">var</span> str = <span class="hljs-string">'hello world'</span>
str <span class="hljs-keyword">instanceof</span> <span class="hljs-built_in">String</span> <span class="hljs-comment">// false</span>
<span class="hljs-keyword">var</span> str1 = <span class="hljs-keyword">new</span> <span class="hljs-built_in">String</span>(<span class="hljs-string">'hello world'</span>)
str1 <span class="hljs-keyword">instanceof</span> <span class="hljs-built_in">String</span> <span class="hljs-comment">// true</span>
</code></pre><p>对于原始类型来说，你想直接通过 <code>instanceof</code> 来判断类型是不行的，当然我们还是有办法让 <code>instanceof</code> 判断原始类型的</p>
<pre><code class="hljs js" lang="js"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">PrimitiveString</span> </span>{
<span class="hljs-keyword">static</span> [<span class="hljs-built_in">Symbol</span>.hasInstance](x) {
<span class="hljs-keyword">return</span> <span class="hljs-keyword">typeof</span> x === <span class="hljs-string">'string'</span>
}
}
<span class="hljs-built_in">console</span>.log(<span class="hljs-string">'hello world'</span> <span class="hljs-keyword">instanceof</span> PrimitiveString) <span class="hljs-comment">// true</span>
</code></pre><p>你可能不知道 <code>Symbol.hasInstance</code> 是什么东西，其实就是一个能让我们自定义 <code>instanceof</code> 行为的东西，以上代码等同于 <code>typeof 'hello world' === 'string'</code>，所以结果自然是 <code>true</code> 了。这其实也侧面反映了一个问题， <code>instanceof</code> 也不是百分之百可信的。</p>
<h2 class="heading" data-id="heading-4">类型转换</h2>
<blockquote class="warning"><p>涉及面试题：该知识点常在笔试题中见到，熟悉了转换规则就不惧怕此类题目了。
</p></blockquote><p>首先我们要知道，在 JS 中类型转换只有三种情况，分别是：</p>
<ul>
<li>转换为布尔值</li>
<li>转换为数字</li>
<li>转换为字符串</li>
</ul>
<p>我们先来看一个类型转换表格，然后再进入正题</p>
<p></p><figure><img class="lazyload inited" data-src="https://user-gold-cdn.xitu.io/2018/11/15/16716dec14421e47?imageView2/0/w/1280/h/960/format/webp/ignore-error/1" data-width="910" data-height="648" src="data:image/svg+xml;utf8,<?xml version="1.0"?><svg xmlns="http://www.w3.org/2000/svg" version="1.1" width="910" height="648"></svg>"><figcaption></figcaption></figure><p></p>
<h3 class="heading" data-id="heading-5">转Boolean</h3>
<p>在条件判断时，除了 <code>undefined</code>， <code>null</code>， <code>false</code>， <code>NaN</code>， <code>''</code>， <code>0</code>， <code>-0</code>，其他所有值都转为 <code>true</code>，包括所有对象。</p>
<h3 class="heading" data-id="heading-6">对象转原始类型</h3>
<p>对象在转换类型的时候，会调用内置的 <code>[[ToPrimitive]]</code> 函数，对于该函数来说，算法逻辑一般来说如下：</p>
<ul>
<li>如果已经是原始类型了，那就不需要转换了</li>
<li>调用 <code>x.valueOf()</code>，如果转换为基础类型，就返回转换的值</li>
<li>调用 <code>x.toString()</code>，如果转换为基础类型，就返回转换的值</li>
<li>如果都没有返回原始类型，就会报错</li>
</ul>
<p>当然你也可以重写 <code>Symbol.toPrimitive</code> ，该方法在转原始类型时调用优先级最高。</p>
<pre><code class="hljs js" lang="js"><span class="hljs-keyword">let</span> a = {
valueOf() {
<span class="hljs-keyword">return</span> <span class="hljs-number">0</span>
},
toString() {
<span class="hljs-keyword">return</span> <span class="hljs-string">'1'</span>
},
[<span class="hljs-built_in">Symbol</span>.toPrimitive]() {
<span class="hljs-keyword">return</span> <span class="hljs-number">2</span>
}
}
<span class="hljs-number">1</span> + a <span class="hljs-comment">// => 3</span>
</code></pre><h3 class="heading" data-id="heading-7">四则运算符</h3>
<p>加法运算符不同于其他几个运算符，它有以下几个特点：</p>
<ul>
<li>运算中其中一方为字符串，那么就会把另一方也转换为字符串</li>
<li>如果一方不是字符串或者数字，那么会将它转换为数字或者字符串</li>
</ul>
<pre><code class="hljs js" lang="js"><span class="hljs-number">1</span> + <span class="hljs-string">'1'</span> <span class="hljs-comment">// '11'</span>
<span class="hljs-literal">true</span> + <span class="hljs-literal">true</span> <span class="hljs-comment">// 2</span>
<span class="hljs-number">4</span> + [<span class="hljs-number">1</span>,<span class="hljs-number">2</span>,<span class="hljs-number">3</span>] <span class="hljs-comment">// "41,2,3"</span>
</code></pre><p>如果你对于答案有疑问的话，请看解析：</p>
<ul>
<li>对于第一行代码来说，触发特点一，所以将数字 <code>1</code> 转换为字符串，得到结果 <code>'11'</code></li>
<li>对于第二行代码来说，触发特点二，所以将 <code>true</code> 转为数字 <code>1</code></li>
<li>对于第三行代码来说，触发特点二，所以将数组通过 <code>toString</code> 转为字符串 <code>1,2,3</code>，得到结果 <code>41,2,3</code></li>
</ul>
<p>另外对于加法还需要注意这个表达式 <code>'a' + + 'b'</code></p>
<pre><code class="hljs js" lang="js"><span class="hljs-string">'a'</span> + + <span class="hljs-string">'b'</span> <span class="hljs-comment">// -> "aNaN"</span>
</code></pre><p>因为 <code>+ 'b'</code> 等于 <code>NaN</code>，所以结果为 <code>"aNaN"</code>，你可能也会在一些代码中看到过 <code>+ '1'</code> 的形式来快速获取 <code>number</code> 类型。</p>
<p>那么对于除了加法的运算符来说，只要其中一方是数字，那么另一方就会被转为数字</p>
<pre><code class="hljs js" lang="js"><span class="hljs-number">4</span> * <span class="hljs-string">'3'</span> <span class="hljs-comment">// 12</span>
<span class="hljs-number">4</span> * [] <span class="hljs-comment">// 0</span>
<span class="hljs-number">4</span> * [<span class="hljs-number">1</span>, <span class="hljs-number">2</span>] <span class="hljs-comment">// NaN</span>
</code></pre><h3 class="heading" data-id="heading-8">比较运算符</h3>
<ol>
<li>如果是对象，就通过 <code>toPrimitive</code> 转换对象</li>
<li>如果是字符串，就通过 <code>unicode</code> 字符索引来比较</li>
</ol>
<pre><code class="hljs js" lang="js"><span class="hljs-keyword">let</span> a = {
valueOf() {
<span class="hljs-keyword">return</span> <span class="hljs-number">0</span>
},
toString() {
<span class="hljs-keyword">return</span> <span class="hljs-string">'1'</span>
}
}
a > <span class="hljs-number">-1</span> <span class="hljs-comment">// true</span>
</code></pre><p>在以上代码中，因为 <code>a</code> 是对象，所以会通过 <code>valueOf</code> 转换为原始类型再比较值。</p>
<h2 class="heading" data-id="heading-9">this</h2>
<blockquote class="warning"><p>涉及面试题：如何正确判断 this？箭头函数的 this 是什么？
</p></blockquote><p><code>this</code> 是很多人会混淆的概念，但是其实它一点都不难，只是网上很多文章把简单的东西说复杂了。在这一小节中，你一定会彻底明白 <code>this</code> 这个概念的。</p>
<p>我们先来看几个函数调用的场景</p>
<pre><code class="hljs js" lang="js"><span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">foo</span>(<span class="hljs-params"></span>) </span>{
<span class="hljs-built_in">console</span>.log(<span class="hljs-keyword">this</span>.a)
}
<span class="hljs-keyword">var</span> a = <span class="hljs-number">1</span>
foo()
<span class="hljs-keyword">const</span> obj = {
<span class="hljs-attr">a</span>: <span class="hljs-number">2</span>,
<span class="hljs-attr">foo</span>: foo
}
obj.foo()
<span class="hljs-keyword">const</span> c = <span class="hljs-keyword">new</span> foo()
</code></pre><p>接下来我们一个个分析上面几个场景</p>
<ul>
<li>对于直接调用 <code>foo</code> 来说，不管 <code>foo</code> 函数被放在了什么地方，<code>this</code> 一定是 <code>window</code></li>
<li>对于 <code>obj.foo()</code> 来说，我们只需要记住，谁调用了函数，谁就是 <code>this</code>，所以在这个场景下 <code>foo</code> 函数中的 <code>this</code> 就是 <code>obj</code> 对象</li>
<li>对于 <code>new</code> 的方式来说，<code>this</code> 被永远绑定在了 <code>c</code> 上面，不会被任何方式改变 <code>this</code></li>
</ul>
<p>说完了以上几种情况，其实很多代码中的 <code>this</code> 应该就没什么问题了，下面让我们看看箭头函数中的 <code>this</code></p>
<pre><code class="hljs js" lang="js"><span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">a</span>(<span class="hljs-params"></span>) </span>{
<span class="hljs-keyword">return</span> <span class="hljs-function"><span class="hljs-params">()</span> =></span> {
<span class="hljs-keyword">return</span> <span class="hljs-function"><span class="hljs-params">()</span> =></span> {
<span class="hljs-built_in">console</span>.log(<span class="hljs-keyword">this</span>)
}
}
}
<span class="hljs-built_in">console</span>.log(a()()())
</code></pre><p>首先箭头函数其实是没有 <code>this</code> 的，箭头函数中的 <code>this</code> 只取决包裹箭头函数的第一个普通函数的 <code>this</code>。在这个例子中，因为包裹箭头函数的第一个普通函数是 <code>a</code>，所以此时的 <code>this</code> 是 <code>window</code>。另外对箭头函数使用 <code>bind</code> 这类函数是无效的。</p>
<p>最后种情况也就是 <code>bind</code> 这些改变上下文的 API 了，对于这些函数来说，<code>this</code> 取决于第一个参数，如果第一个参数为空，那么就是 <code>window</code>。</p>
<p>那么说到 <code>bind</code>，不知道大家是否考虑过，如果对一个函数进行多次 <code>bind</code>，那么上下文会是什么呢？</p>
<pre><code class="hljs js" lang="js"><span class="hljs-keyword">let</span> a = {}
<span class="hljs-keyword">let</span> fn = <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{ <span class="hljs-built_in">console</span>.log(<span class="hljs-keyword">this</span>) }
fn.bind().bind(a)() <span class="hljs-comment">// => ?</span>
</code></pre><p>如果你认为输出结果是 <code>a</code>，那么你就错了，其实我们可以把上述代码转换成另一种形式</p>
<pre><code class="hljs js" lang="js"><span class="hljs-comment">// fn.bind().bind(a) 等于</span>
<span class="hljs-keyword">let</span> fn2 = <span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">fn1</span>(<span class="hljs-params"></span>) </span>{
<span class="hljs-keyword">return</span> <span class="hljs-function"><span class="hljs-keyword">function</span>(<span class="hljs-params"></span>) </span>{
<span class="hljs-keyword">return</span> fn.apply()
}.apply(a)
}
fn2()
</code></pre><p>可以从上述代码中发现，不管我们给函数 <code>bind</code> 几次，<code>fn</code> 中的 <code>this</code> 永远由第一次 <code>bind</code> 决定，所以结果永远是 <code>window</code>。</p>
<pre><code class="hljs js" lang="js"><span class="hljs-keyword">let</span> a = { <span class="hljs-attr">name</span>: <span class="hljs-string">'yck'</span> }
<span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">foo</span>(<span class="hljs-params"></span>) </span>{
<span class="hljs-built_in">console</span>.log(<span class="hljs-keyword">this</span>.name)
}
foo.bind(a)() <span class="hljs-comment">// => 'yck'</span>
</code></pre><p>以上就是 <code>this</code> 的规则了，但是可能会发生多个规则同时出现的情况，这时候不同的规则之间会根据优先级最高的来决定 <code>this</code> 最终指向哪里。</p>
<p>首先，<code>new</code> 的方式优先级最高，接下来是 <code>bind</code> 这些函数，然后是 <code>obj.foo()</code> 这种调用方式，最后是 <code>foo</code> 这种调用方式，同时，箭头函数的 <code>this</code> 一旦被绑定，就不会再被任何方式所改变。</p>
<p>如果你还是觉得有点绕，那么就看以下的这张流程图吧，图中的流程只针对于单个规则。</p>
<p></p><figure><img class="lazyload inited" data-src="https://user-gold-cdn.xitu.io/2018/11/15/16717eaf3383aae8?imageView2/0/w/1280/h/960/format/webp/ignore-error/1" data-width="744" data-height="531" src="data:image/svg+xml;utf8,<?xml version="1.0"?><svg xmlns="http://www.w3.org/2000/svg" version="1.1" width="744" height="531"></svg>"><figcaption></figcaption></figure><p></p>
<h2 class="heading" data-id="heading-10">小结</h2>
<p>以上就是我们 JS 基础知识点的第一部分内容了。这一小节中涉及到的知识点在我们日常的开发中经常可以看到，并且很多容易出现的坑 也出自于这些知识点，相信认真读完的你一定会在日后的开发中少踩很多坑。如果大家对于这个章节的内容存在疑问，欢迎在评论区与我互动。</p>
</div><section data-v-ecce5e7e="" class="book-comments"><div data-v-ecce5e7e="" class="box-title">留言</div><div data-v-ecce5e7e="" class="comment-box"><div data-v-1146c0e6="" data-v-ecce5e7e="" class="comment-form comment-form" id="comment"><div data-v-57c47624="" data-v-cf310dfc="" data-v-1146c0e6="" data-src="https://avatars0.githubusercontent.com/u/33979626?v=4" class="lazy avatar avatar loaded" style="background-image: url("https://avatars0.githubusercontent.com/u/33979626?v=4");"></div><textarea data-v-1146c0e6="" placeholder="评论将在后台进行审核，审核通过后对所有人可见" class="content-input" style="overflow: hidden; overflow-wrap: break-word; height: 60px;"></textarea><div data-v-1146c0e6="" class="action-box" style="display: none;"><div data-v-627e3889="" data-v-1146c0e6="" class="image-uploader image-uploader" style="display: none;"><input data-v-627e3889="" type="file" class="input"><button data-v-627e3889="" class="upload-btn"><i data-v-627e3889="" class="icon ion-image"></i><span data-v-627e3889="">上传图片</span></button></div><div data-v-1146c0e6="" class="submit-box"><span data-v-1146c0e6="" class="submit-text">Ctrl or ⌘ + Enter</span><button data-v-1146c0e6="" class="submit-btn">评论</button></div></div><!----></div></div><ul data-v-6adae277="" data-v-ecce5e7e="" st:block="commentList" class="comment-list comment-list"><li data-v-6adae277="" class="item"><div data-v-38783431="" data-v-6adae277="" class="comment"><div data-v-3a6943ce="" data-v-38783431="" st:block="userPopover" st:state="5712832f128fe1006cee5f3c" class="user-popover-box"><!----><a data-v-38783431="" href="https://juejin.im/user/5712832f128fe1006cee5f3c" target="_blank" rel="" data-v-3a6943ce=""><div data-v-57c47624="" data-v-cf310dfc="" data-v-38783431="" data-src="https://user-gold-cdn.xitu.io/2017/8/25/e6bc0347fe0ec61cb2362ddcb665bd60?imageView2/1/w/100/h/100/q/85/format/webp/interlace/1" class="lazy avatar avatar" style="background-image: none;"></div></a></div><div data-v-38783431="" class="content-box"><div data-v-38783431="" class="header"><div data-v-38783431="" class="user-info"><div data-v-3a6943ce="" data-v-38783431="" st:block="userPopover" st:state="5712832f128fe1006cee5f3c" class="user-popover-box"><!----><a data-v-38783431="" href="https://juejin.im/user/5712832f128fe1006cee5f3c" target="_blank" rel="" class="username" data-v-3a6943ce="">永孩儿</a></div><div data-v-38783431="" class="position"></div></div></div><div data-v-38783431="" class="content"><!----><span data-v-38783431="" class="content-html">感受到了满满的干货，同时说明我基础薄弱，赞</span><!----></div><div data-v-38783431="" class="footer"><button data-v-38783431="" class="like-btn"><i data-v-38783431="" class="collection-arrow-ion ion-arrow-up-b"></i><span data-v-38783431="">0</span></button><span data-v-38783431="" class="sub-comment-btn text-pointer"><span data-v-38783431="" class="title">评论</span><div data-v-38783431="" class="sub-comment--arrow" style="display: none;"></div></span><span data-v-38783431="" class="date">1小时前</span><!----></div><!----></div><!----></div></li><li data-v-6adae277="" class="item"><div data-v-38783431="" data-v-6adae277="" class="comment"><div data-v-3a6943ce="" data-v-38783431="" st:block="userPopover" st:state="5adf202af265da0b84551306" class="user-popover-box"><!----><a data-v-38783431="" href="https://juejin.im/user/5adf202af265da0b84551306" target="_blank" rel="" data-v-3a6943ce=""><div data-v-57c47624="" data-v-cf310dfc="" data-v-38783431="" data-src="https://user-gold-cdn.xitu.io/2019/1/8/1682cdf36e80f675?imageView2/1/w/100/h/100/q/85/format/webp/interlace/1" class="lazy avatar avatar loaded" style="background-image: url("https://user-gold-cdn.xitu.io/2019/1/8/1682cdf36e80f675?imageView2/1/w/100/h/100/q/85/format/webp/interlace/1");"></div></a></div><div data-v-38783431="" class="content-box"><div data-v-38783431="" class="header"><div data-v-38783431="" class="user-info"><div data-v-3a6943ce="" data-v-38783431="" st:block="userPopover" st:state="5adf202af265da0b84551306" class="user-popover-box"><!----><a data-v-38783431="" href="https://juejin.im/user/5adf202af265da0b84551306" target="_blank" rel="" class="username" data-v-3a6943ce="">wq93</a></div><div data-v-38783431="" class="position">前端工程师</div></div></div><div data-v-38783431="" class="content"><!----><span data-v-38783431="" class="content-html">四则运算符
加法运算符不同于其他几个运算符，它有以下几个特点：
运算中其中一方为字符串，那么就会把另一方也转换为字符串
如果一方不是字符串或者数字，那么会将它转换为数字或者字符串
"如果一方不是字符串或者数字，那么会将它转换为数字或者字符串
" 感觉这个总结的有问题,如果是引用类型的话应该是调用toPrimitive规则</span><!----></div><div data-v-38783431="" class="footer"><button data-v-38783431="" class="like-btn"><i data-v-38783431="" class="collection-arrow-ion ion-arrow-up-b"></i><span data-v-38783431="">0</span></button><span data-v-38783431="" class="sub-comment-btn text-pointer"><span data-v-38783431="" class="title">评论</span><div data-v-38783431="" class="sub-comment--arrow" style="display: none;"></div></span><span data-v-38783431="" class="date">23小时前</span><!----></div><!----></div><!----></div></li><li data-v-6adae277="" class="item"><div data-v-38783431="" data-v-6adae277="" class="comment"><div data-v-3a6943ce="" data-v-38783431="" st:block="userPopover" st:state="5b1108286fb9a01e3e5cdd62" class="user-popover-box"><!----><a data-v-38783431="" href="https://juejin.im/user/5b1108286fb9a01e3e5cdd62" target="_blank" rel="" data-v-3a6943ce=""><div data-v-57c47624="" data-v-cf310dfc="" data-v-38783431="" data-src="https://user-gold-cdn.xitu.io/2019/1/3/16811f6575375832?imageView2/1/w/100/h/100/q/85/format/webp/interlace/1" class="lazy avatar avatar" style="background-image: none;"></div></a></div><div data-v-38783431="" class="content-box"><div data-v-38783431="" class="header"><div data-v-38783431="" class="user-info"><div data-v-3a6943ce="" data-v-38783431="" st:block="userPopover" st:state="5b1108286fb9a01e3e5cdd62" class="user-popover-box"><!----><a data-v-38783431="" href="https://juejin.im/user/5b1108286fb9a01e3e5cdd62" target="_blank" rel="" class="username" data-v-3a6943ce="">被清晨的馬路寵愛著</a></div><div data-v-38783431="" class="position">前端实习生 @ 上海中期期货股份有限公司</div></div></div><div data-v-38783431="" class="content"><!----><span data-v-38783431="" class="content-html">正在看</span><!----></div><div data-v-38783431="" class="footer"><button data-v-38783431="" class="like-btn"><i data-v-38783431="" class="collection-arrow-ion ion-arrow-up-b"></i><span data-v-38783431="">0</span></button><span data-v-38783431="" class="sub-comment-btn text-pointer"><span data-v-38783431="" class="title">评论</span><div data-v-38783431="" class="sub-comment--arrow" style="display: none;"></div></span><span data-v-38783431="" class="date">2天前</span><!----></div><!----></div><!----></div></li><li data-v-6adae277="" class="item"><div data-v-38783431="" data-v-6adae277="" class="comment"><div data-v-3a6943ce="" data-v-38783431="" st:block="userPopover" st:state="5bc3d8206fb9a05ce37b1fae" class="user-popover-box"><!----><a data-v-38783431="" href="https://juejin.im/user/5bc3d8206fb9a05ce37b1fae" target="_blank" rel="" data-v-3a6943ce=""><div data-v-57c47624="" data-v-cf310dfc="" data-v-38783431="" data-src="https://user-gold-cdn.xitu.io/2018/10/15/1667564f88eb5d2d?imageView2/1/w/100/h/100/q/85/format/webp/interlace/1" class="lazy avatar avatar" style="background-image: none;"></div></a></div><div data-v-38783431="" class="content-box"><div data-v-38783431="" class="header"><div data-v-38783431="" class="user-info"><div data-v-3a6943ce="" data-v-38783431="" st:block="userPopover" st:state="5bc3d8206fb9a05ce37b1fae" class="user-popover-box"><!----><a data-v-38783431="" href="https://juejin.im/user/5bc3d8206fb9a05ce37b1fae" target="_blank" rel="" class="username" data-v-3a6943ce="">枯木朽株</a></div><div data-v-38783431="" class="position">web前端 @ 杭州诚淘电商</div></div></div><div data-v-38783431="" class="content"><!----><span data-v-38783431="" class="content-html">第一次比较全面的了解了this的指向问题</span><!----></div><div data-v-38783431="" class="footer"><button data-v-38783431="" class="like-btn"><i data-v-38783431="" class="collection-arrow-ion ion-arrow-up-b"></i><span data-v-38783431="">0</span></button><span data-v-38783431="" class="sub-comment-btn text-pointer"><span data-v-38783431="" class="title">评论</span><div data-v-38783431="" class="sub-comment--arrow" style="display: none;"></div></span><span data-v-38783431="" class="date">3天前</span><!----></div><!----></div><!----></div></li><li data-v-6adae277="" class="item"><div data-v-38783431="" data-v-6adae277="" class="comment"><div data-v-3a6943ce="" data-v-38783431="" st:block="userPopover" st:state="5800c5b267f3560058a9f89f" class="user-popover-box"><!----><a data-v-38783431="" href="https://juejin.im/user/5800c5b267f3560058a9f89f" target="_blank" rel="" data-v-3a6943ce=""><div data-v-57c47624="" data-v-cf310dfc="" data-v-38783431="" data-src="https://user-gold-cdn.xitu.io/2018/10/30/166c3cdb0ebfd2b9?imageView2/1/w/100/h/100/q/85/format/webp/interlace/1" class="lazy avatar avatar" style="background-image: none;"></div></a></div><div data-v-38783431="" class="content-box"><div data-v-38783431="" class="header"><div data-v-38783431="" class="user-info"><div data-v-3a6943ce="" data-v-38783431="" st:block="userPopover" st:state="5800c5b267f3560058a9f89f" class="user-popover-box"><!----><a data-v-38783431="" href="https://juejin.im/user/5800c5b267f3560058a9f89f" target="_blank" rel="" class="username" data-v-3a6943ce="">AddOneG</a></div><div data-v-38783431="" class="position">前端 @ 小学二年级</div></div></div><div data-v-38783431="" class="content"><!----><span data-v-38783431="" class="content-html">讲的一般</span><!----></div><div data-v-38783431="" class="footer"><button data-v-38783431="" class="like-btn"><i data-v-38783431="" class="collection-arrow-ion ion-arrow-up-b"></i><span data-v-38783431="">4</span></button><span data-v-38783431="" class="sub-comment-btn text-pointer"><span data-v-38783431="" class="title">评论</span><div data-v-38783431="" class="sub-comment--arrow" style="display: none;"></div></span><span data-v-38783431="" class="date">4天前</span><!----></div><!----></div><!----></div></li><li data-v-6adae277="" class="item"><div data-v-38783431="" data-v-6adae277="" class="comment"><div data-v-3a6943ce="" data-v-38783431="" st:block="userPopover" st:state="592ff0572f301e006bcc313f" class="user-popover-box"><!----><a data-v-38783431="" href="https://juejin.im/user/592ff0572f301e006bcc313f" target="_blank" rel="" data-v-3a6943ce=""><div data-v-57c47624="" data-v-cf310dfc="" data-v-38783431="" data-src="https://avatars2.githubusercontent.com/u/22095365?v=3" class="lazy avatar avatar" style="background-image: none;"></div></a></div><div data-v-38783431="" class="content-box"><div data-v-38783431="" class="header"><div data-v-38783431="" class="user-info"><div data-v-3a6943ce="" data-v-38783431="" st:block="userPopover" st:state="592ff0572f301e006bcc313f" class="user-popover-box"><!----><a data-v-38783431="" href="https://juejin.im/user/592ff0572f301e006bcc313f" target="_blank" rel="" class="username" data-v-3a6943ce="">jinlong</a></div><div data-v-38783431="" class="position"></div></div></div><div data-v-38783431="" class="content"><!----><span data-v-38783431="" class="content-html">这个this图牛逼了</span><!----></div><div data-v-38783431="" class="footer"><button data-v-38783431="" class="like-btn"><i data-v-38783431="" class="collection-arrow-ion ion-arrow-up-b"></i><span data-v-38783431="">1</span></button><span data-v-38783431="" class="sub-comment-btn text-pointer"><span data-v-38783431="" class="title">评论</span><div data-v-38783431="" class="sub-comment--arrow" style="display: none;"></div></span><span data-v-38783431="" class="date">4天前</span><!----></div><!----></div><!----></div></li><li data-v-6adae277="" class="item"><div data-v-38783431="" data-v-6adae277="" class="comment"><div data-v-3a6943ce="" data-v-38783431="" st:block="userPopover" st:state="58edc26561ff4b00581ab586" class="user-popover-box"><!----><a data-v-38783431="" href="https://juejin.im/user/58edc26561ff4b00581ab586" target="_blank" rel="" data-v-3a6943ce=""><div data-v-57c47624="" data-v-cf310dfc="" data-v-38783431="" data-src="https://user-gold-cdn.xitu.io/2017/4/12/cc1a127e610ffd20ffa8afd7189cacd5.jpg?imageView2/1/w/100/h/100/q/85/format/webp/interlace/1" class="lazy avatar avatar" style="background-image: none;"></div></a></div><div data-v-38783431="" class="content-box"><div data-v-38783431="" class="header"><div data-v-38783431="" class="user-info"><div data-v-3a6943ce="" data-v-38783431="" st:block="userPopover" st:state="58edc26561ff4b00581ab586" class="user-popover-box"><!----><a data-v-38783431="" href="https://juejin.im/user/58edc26561ff4b00581ab586" target="_blank" rel="" class="username" data-v-3a6943ce="">sugusGeek</a></div><div data-v-38783431="" class="position">web前端开发 @ 指点教育</div></div></div><div data-v-38783431="" class="content"><!----><span data-v-38783431="" class="content-html">1.四则运算符的减法没有讲到哦，个加法还是不一样的，却更趋向于乘除法！2.隐式类型转换要是加入算式运算符和逻辑运算符后的混合运算，可以讲下哈！3.new Number 和 number , new String和string这种原始类型和对象类型的比较，哪些地方会用到，差异又在哪里！</span><!----></div><div data-v-38783431="" class="footer"><button data-v-38783431="" class="like-btn"><i data-v-38783431="" class="collection-arrow-ion ion-arrow-up-b"></i><span data-v-38783431="">0</span></button><span data-v-38783431="" class="sub-comment-btn text-pointer"><span data-v-38783431="" class="title">评论</span><div data-v-38783431="" class="sub-comment--arrow" style="display: none;"></div></span><span data-v-38783431="" class="date">4天前</span><!----></div><!----></div><!----></div></li><li data-v-6adae277="" class="item"><div data-v-38783431="" data-v-6adae277="" class="comment"><div data-v-3a6943ce="" data-v-38783431="" st:block="userPopover" st:state="5bd02abb5188252f4f600569" class="user-popover-box"><!----><a data-v-38783431="" href="https://juejin.im/user/5bd02abb5188252f4f600569" target="_blank" rel="" data-v-3a6943ce=""><div data-v-57c47624="" data-v-cf310dfc="" data-v-38783431="" data-src="https://user-gold-cdn.xitu.io/2019/1/6/1681f1b8532d42c6?imageView2/1/w/100/h/100/q/85/format/webp/interlace/1" class="lazy avatar avatar" style="background-image: none;"></div></a></div><div data-v-38783431="" class="content-box"><div data-v-38783431="" class="header"><div data-v-38783431="" class="user-info"><div data-v-3a6943ce="" data-v-38783431="" st:block="userPopover" st:state="5bd02abb5188252f4f600569" class="user-popover-box"><!----><a data-v-38783431="" href="https://juejin.im/user/5bd02abb5188252f4f600569" target="_blank" rel="" class="username" data-v-3a6943ce="">wscfan</a></div><div data-v-38783431="" class="position">前端工程师</div></div></div><div data-v-38783431="" class="content"><!----><span data-v-38783431="" class="content-html">跟着大佬走，没错。</span><!----></div><div data-v-38783431="" class="footer"><button data-v-38783431="" class="like-btn"><i data-v-38783431="" class="collection-arrow-ion ion-arrow-up-b"></i><span data-v-38783431="">0</span></button><span data-v-38783431="" class="sub-comment-btn text-pointer"><span data-v-38783431="" class="title">评论</span><div data-v-38783431="" class="sub-comment--arrow" style="display: none;"></div></span><span data-v-38783431="" class="date">5天前</span><!----></div><!----></div><!----></div></li><li data-v-6adae277="" class="item"><div data-v-38783431="" data-v-6adae277="" class="comment"><div data-v-3a6943ce="" data-v-38783431="" st:block="userPopover" st:state="5c2342a96fb9a04a04411142" class="user-popover-box"><!----><a data-v-38783431="" href="https://juejin.im/user/5c2342a96fb9a04a04411142" target="_blank" rel="" data-v-3a6943ce=""><div data-v-57c47624="" data-v-cf310dfc="" data-v-38783431="" data-src="https://thirdwx.qlogo.cn/mmopen/vi_32/cgMvzeAIKqgDYt5Y6giaKFdboEgFYsylbt2iaA2MMKiazo6RmicdLnic8cIB0IjyYia5AGlXj8rea2yWa2NYqOcb3mdg/132" class="lazy avatar avatar" style="background-image: none;"></div></a></div><div data-v-38783431="" class="content-box"><div data-v-38783431="" class="header"><div data-v-38783431="" class="user-info"><div data-v-3a6943ce="" data-v-38783431="" st:block="userPopover" st:state="5c2342a96fb9a04a04411142" class="user-popover-box"><!----><a data-v-38783431="" href="https://juejin.im/user/5c2342a96fb9a04a04411142" target="_blank" rel="" class="username" data-v-3a6943ce="">刘飞｜工作</a></div><div data-v-38783431="" class="position"></div></div></div><div data-v-38783431="" class="content"><!----><span data-v-38783431="" class="content-html"><a href="https://link.juejin.im/?target=https%3A%2F%2Fgithub.com%2Fmqyqingfeng%2FBlog%2Fissues%2F10" target="_blank" rel="nofollow noopener noreferrer">https://github.com/mqyqingfeng/Blog/issues/10</a></span><!----></div><div data-v-38783431="" class="footer"><button data-v-38783431="" class="like-btn"><i data-v-38783431="" class="collection-arrow-ion ion-arrow-up-b"></i><span data-v-38783431="">0</span></button><span data-v-38783431="" class="sub-comment-btn text-pointer"><span data-v-38783431="" class="title">评论</span><div data-v-38783431="" class="sub-comment--arrow" style="display: none;"></div></span><span data-v-38783431="" class="date">6天前</span><!----></div><!----></div><!----></div></li><li data-v-6adae277="" class="item"><div data-v-38783431="" data-v-6adae277="" class="comment"><div data-v-3a6943ce="" data-v-38783431="" st:block="userPopover" st:state="5bb6114cf265da0b001f459f" class="user-popover-box"><!----><a data-v-38783431="" href="https://juejin.im/user/5bb6114cf265da0b001f459f" target="_blank" rel="" data-v-3a6943ce=""><div data-v-57c47624="" data-v-cf310dfc="" data-v-38783431="" data-src="https://tva2.sinaimg.cn/crop.14.0.722.722.180/9fd00fabjw8fag85y8jqqj20ku0k2dgp.jpg" class="lazy avatar avatar" style="background-image: none;"></div></a></div><div data-v-38783431="" class="content-box"><div data-v-38783431="" class="header"><div data-v-38783431="" class="user-info"><div data-v-3a6943ce="" data-v-38783431="" st:block="userPopover" st:state="5bb6114cf265da0b001f459f" class="user-popover-box"><!----><a data-v-38783431="" href="https://juejin.im/user/5bb6114cf265da0b001f459f" target="_blank" rel="" class="username" data-v-3a6943ce="">希望and现实</a></div><div data-v-38783431="" class="position"></div></div></div><div data-v-38783431="" class="content"><!----><span data-v-38783431="" class="content-html">const p2 = test(p1)那边不就是返回preson嘛...没看出和指针有什么关系...还是我漏掉什么了</span><!----></div><div data-v-38783431="" class="footer"><button data-v-38783431="" class="like-btn"><i data-v-38783431="" class="collection-arrow-ion ion-arrow-up-b"></i><span data-v-38783431="">0</span></button><span data-v-38783431="" class="sub-comment-btn text-pointer"><span data-v-38783431="" class="title">收起评论</span><div data-v-38783431="" class="sub-comment--arrow" style=""></div></span><span data-v-38783431="" class="date">6天前</span><!----></div><div data-v-4afc11f9="" data-v-38783431="" class="sub-comment-box sub-comment-box"><div data-v-4afc11f9="" class="sub-comment-box__top"><div data-v-4afc11f9="" class="icon-close"></div><h3 data-v-4afc11f9="">评论</h3></div><div data-v-4afc11f9="" class="sub-comment-box__inner"><div data-v-4afc11f9=""><ul data-v-4afc11f9="" class="sub-comment-list"><li data-v-4afc11f9="" class="item"><div data-v-6fd44370="" data-v-4afc11f9="" class="sub-comment sub-comment"><div data-v-3a6943ce="" data-v-6fd44370="" st:block="userPopover" st:state="5adf202af265da0b84551306" class="user-popover-box user-popover--avatar"><!----><div data-v-57c47624="" data-v-cf310dfc="" data-v-6fd44370="" data-src="https://user-gold-cdn.xitu.io/2019/1/8/1682cdf36e80f675?imageView2/1/w/100/h/100/q/85/format/webp/interlace/1" class="lazy avatar avatar loaded" data-v-3a6943ce="" style="background-image: url("https://user-gold-cdn.xitu.io/2019/1/8/1682cdf36e80f675?imageView2/1/w/100/h/100/q/85/format/webp/interlace/1");"></div></div><div data-v-6fd44370="" class="content-box"><div data-v-6fd44370="" class="header"><div data-v-6fd44370="" class="user-info"><div data-v-3a6943ce="" data-v-6fd44370="" st:block="userPopover" st:state="5adf202af265da0b84551306" class="user-popover-box user-popover--info"><!----><a data-v-6fd44370="" href="https://juejin.im/user/5adf202af265da0b84551306" target="_blank" rel="" class="username" data-v-3a6943ce="">wq93</a></div><div data-v-6fd44370="" class="position">前端工程师</div></div></div><div data-v-6fd44370="" class="content"><!----><span data-v-6fd44370="" class="content-html">person = {...}重新赋值了</span><!----></div><div data-v-6fd44370="" class="footer"><span data-v-6fd44370="" class="date">6天前</span><a data-v-6fd44370="" class="reply-btn">回复</a><!----></div></div><!----></div></li><li data-v-4afc11f9="" class="item"><div data-v-6fd44370="" data-v-4afc11f9="" class="sub-comment sub-comment"><div data-v-3a6943ce="" data-v-6fd44370="" st:block="userPopover" st:state="574d2f2a2e958a00693487b0" class="user-popover-box user-popover--avatar"><!----><div data-v-57c47624="" data-v-cf310dfc="" data-v-6fd44370="" data-src="https://user-gold-cdn.xitu.io/2016/11/29/1f8696de1b039644cd832953cca8f38d?imageView2/1/w/100/h/100/q/85/format/webp/interlace/1" class="lazy avatar avatar" data-v-3a6943ce="" style="background-image: none;"></div></div><div data-v-6fd44370="" class="content-box"><div data-v-6fd44370="" class="header"><div data-v-6fd44370="" class="user-info"><div data-v-3a6943ce="" data-v-6fd44370="" st:block="userPopover" st:state="574d2f2a2e958a00693487b0" class="user-popover-box user-popover--info"><!----><a data-v-6fd44370="" href="https://juejin.im/user/574d2f2a2e958a00693487b0" target="_blank" rel="" class="username" data-v-3a6943ce="">旅梦开发团</a></div><div data-v-6fd44370="" class="position">创始人 @ 旅梦开发团</div></div></div><div data-v-6fd44370="" class="content"><!----><span data-v-6fd44370="" class="content-html">当p1传给test函数里面第一句代码就是利用了指针person和p1指向相同的地址，然后person再指向另外一个地址</span><!----></div><div data-v-6fd44370="" class="footer"><span data-v-6fd44370="" class="date">5天前</span><a data-v-6fd44370="" class="reply-btn">回复</a><!----></div></div><!----></div></li><li data-v-4afc11f9="" class="item"><div data-v-6fd44370="" data-v-4afc11f9="" class="sub-comment sub-comment"><div data-v-3a6943ce="" data-v-6fd44370="" st:block="userPopover" st:state="5bb6114cf265da0b001f459f" class="user-popover-box user-popover--avatar"><!----><div data-v-57c47624="" data-v-cf310dfc="" data-v-6fd44370="" data-src="https://tva2.sinaimg.cn/crop.14.0.722.722.180/9fd00fabjw8fag85y8jqqj20ku0k2dgp.jpg" class="lazy avatar avatar" data-v-3a6943ce="" style="background-image: none;"></div></div><div data-v-6fd44370="" class="content-box"><div data-v-6fd44370="" class="header"><div data-v-6fd44370="" class="user-info"><div data-v-3a6943ce="" data-v-6fd44370="" st:block="userPopover" st:state="5bb6114cf265da0b001f459f" class="user-popover-box user-popover--info"><!----><a data-v-6fd44370="" href="https://juejin.im/user/5bb6114cf265da0b001f459f" target="_blank" rel="" class="username" data-v-3a6943ce="">希望and现实</a></div><div data-v-6fd44370="" class="position"></div></div></div><div data-v-6fd44370="" class="content"><span data-v-6fd44370="" class="text-reply">回复<a data-v-6fd44370="" href="https://juejin.im/user/574d2f2a2e958a00693487b0" target="_blank" rel=""><span data-v-6fd44370="" class="username">旅梦开发团</span></a>：</span><span data-v-6fd44370="" class="content-html">我指了解过一点点c，这里的意思是function里的指针是没有固定指向的嘛？</span><!----></div><div data-v-6fd44370="" class="footer"><span data-v-6fd44370="" class="date">5天前</span><a data-v-6fd44370="" class="reply-btn">回复</a><!----></div></div><!----></div></li></ul><!----></div><form data-v-4afc11f9="" class="reply-form"><textarea data-v-4afc11f9="" rows="1" maxlength="1024" placeholder="评论审核通过后显示" style="overflow: hidden; overflow-wrap: break-word; height: 35px;"></textarea><button data-v-4afc11f9="" class="reply-btn">评论</button></form></div></div></div><!----></div></li><li data-v-6adae277="" class="item"><div data-v-38783431="" data-v-6adae277="" class="comment"><div data-v-3a6943ce="" data-v-38783431="" st:block="userPopover" st:state="5bd044496fb9a05d1658c8ea" class="user-popover-box"><!----><a data-v-38783431="" href="https://juejin.im/user/5bd044496fb9a05d1658c8ea" target="_blank" rel="" data-v-3a6943ce=""><div data-v-57c47624="" data-v-cf310dfc="" data-v-38783431="" data-src="https://thirdwx.qlogo.cn/mmopen/vi_32/0RbBItibyUk6mvbfISP4TCuUZiaeuZBacWxxL35h2413H92B4AHS9BWscBdt2ibAxYgtmgFRfN3Hia65iafJK9KBnqg/132" class="lazy avatar avatar" style="background-image: none;"></div></a></div><div data-v-38783431="" class="content-box"><div data-v-38783431="" class="header"><div data-v-38783431="" class="user-info"><div data-v-3a6943ce="" data-v-38783431="" st:block="userPopover" st:state="5bd044496fb9a05d1658c8ea" class="user-popover-box"><!----><a data-v-38783431="" href="https://juejin.im/user/5bd044496fb9a05d1658c8ea" target="_blank" rel="" class="username" data-v-3a6943ce="">诺诺同志</a></div><div data-v-38783431="" class="position"></div></div></div><div data-v-38783431="" class="content"><!----><span data-v-38783431="" class="content-html">确实牛批</span><!----></div><div data-v-38783431="" class="footer"><button data-v-38783431="" class="like-btn"><i data-v-38783431="" class="collection-arrow-ion ion-arrow-up-b"></i><span data-v-38783431="">0</span></button><span data-v-38783431="" class="sub-comment-btn text-pointer"><span data-v-38783431="" class="title">评论</span><div data-v-38783431="" class="sub-comment--arrow" style="display: none;"></div></span><span data-v-38783431="" class="date">7天前</span><!----></div><!----></div><!----></div></li><li data-v-6adae277="" class="item"><div data-v-38783431="" data-v-6adae277="" class="comment"><div data-v-3a6943ce="" data-v-38783431="" st:block="userPopover" st:state="5c1ed9216fb9a04a0f652ae5" class="user-popover-box"><!----><a data-v-38783431="" href="https://juejin.im/user/5c1ed9216fb9a04a0f652ae5" target="_blank" rel="" data-v-3a6943ce=""><div data-v-57c47624="" data-v-cf310dfc="" data-v-38783431="" data-src="https://user-gold-cdn.xitu.io/2018/12/23/167d88131f954a9f?imageView2/1/w/100/h/100/q/85/format/webp/interlace/1" class="lazy avatar avatar" style="background-image: none;"></div></a></div><div data-v-38783431="" class="content-box"><div data-v-38783431="" class="header"><div data-v-38783431="" class="user-info"><div data-v-3a6943ce="" data-v-38783431="" st:block="userPopover" st:state="5c1ed9216fb9a04a0f652ae5" class="user-popover-box"><!----><a data-v-38783431="" href="https://juejin.im/user/5c1ed9216fb9a04a0f652ae5" target="_blank" rel="" class="username" data-v-3a6943ce="">Rockj</a></div><div data-v-38783431="" class="position">前端工程师 @ 存勖科技</div></div></div><div data-v-38783431="" class="content"><!----><span data-v-38783431="" class="content-html">好流弊啊</span><!----></div><div data-v-38783431="" class="footer"><button data-v-38783431="" class="like-btn"><i data-v-38783431="" class="collection-arrow-ion ion-arrow-up-b"></i><span data-v-38783431="">0</span></button><span data-v-38783431="" class="sub-comment-btn text-pointer"><span data-v-38783431="" class="title">评论</span><div data-v-38783431="" class="sub-comment--arrow" style="display: none;"></div></span><span data-v-38783431="" class="date">8天前</span><!----></div><!----></div><!----></div></li><li data-v-6adae277="" class="item"><div data-v-38783431="" data-v-6adae277="" class="comment"><div data-v-3a6943ce="" data-v-38783431="" st:block="userPopover" st:state="5b38b43ee51d45589d67f498" class="user-popover-box"><!----><a data-v-38783431="" href="https://juejin.im/user/5b38b43ee51d45589d67f498" target="_blank" rel="" data-v-3a6943ce=""><div data-v-57c47624="" data-v-cf310dfc="" data-v-38783431="" data-src="https://thirdwx.qlogo.cn/mmopen/vi_32/Q0j4TwGTfTK7DepRj94lyz4O9Fibria1cN9rJW8AKlQnLbL8brjLVgQWluDcCG0twricUAzichxcwz7vXgfIOib6R9g/132" class="lazy avatar avatar" style="background-image: none;"></div></a></div><div data-v-38783431="" class="content-box"><div data-v-38783431="" class="header"><div data-v-38783431="" class="user-info"><div data-v-3a6943ce="" data-v-38783431="" st:block="userPopover" st:state="5b38b43ee51d45589d67f498" class="user-popover-box"><!----><a data-v-38783431="" href="https://juejin.im/user/5b38b43ee51d45589d67f498" target="_blank" rel="" class="username" data-v-3a6943ce="">lucahan在搞GIS</a></div><div data-v-38783431="" class="position">低级API工程师 @ 华南光电科技公司</div></div></div><div data-v-38783431="" class="content"><!----><span data-v-38783431="" class="content-html">为什么true+true的结果是2，而不是'truetrue'呢？</span><!----></div><div data-v-38783431="" class="footer"><button data-v-38783431="" class="like-btn"><i data-v-38783431="" class="collection-arrow-ion ion-arrow-up-b"></i><span data-v-38783431="">3</span></button><span data-v-38783431="" class="sub-comment-btn text-pointer"><span data-v-38783431="" class="title">收起评论</span><div data-v-38783431="" class="sub-comment--arrow" style=""></div></span><span data-v-38783431="" class="date">11天前</span><!----></div><div data-v-4afc11f9="" data-v-38783431="" class="sub-comment-box sub-comment-box"><div data-v-4afc11f9="" class="sub-comment-box__top"><div data-v-4afc11f9="" class="icon-close"></div><h3 data-v-4afc11f9="">评论</h3></div><div data-v-4afc11f9="" class="sub-comment-box__inner"><div data-v-4afc11f9=""><ul data-v-4afc11f9="" class="sub-comment-list"><li data-v-4afc11f9="" class="item"><div data-v-6fd44370="" data-v-4afc11f9="" class="sub-comment sub-comment"><div data-v-3a6943ce="" data-v-6fd44370="" st:block="userPopover" st:state="5b0e60f6f265da08f0339162" class="user-popover-box user-popover--avatar"><!----><div data-v-57c47624="" data-v-cf310dfc="" data-v-6fd44370="" data-src="https://user-gold-cdn.xitu.io/2018/8/3/164fdd0cb5708bf0?imageView2/1/w/100/h/100/q/85/format/webp/interlace/1" class="lazy avatar avatar" data-v-3a6943ce="" style="background-image: none;"></div></div><div data-v-6fd44370="" class="content-box"><div data-v-6fd44370="" class="header"><div data-v-6fd44370="" class="user-info"><div data-v-3a6943ce="" data-v-6fd44370="" st:block="userPopover" st:state="5b0e60f6f265da08f0339162" class="user-popover-box user-popover--info"><!----><a data-v-6fd44370="" href="https://juejin.im/user/5b0e60f6f265da08f0339162" target="_blank" rel="" class="username" data-v-3a6943ce="">dsying</a></div><div data-v-6fd44370="" class="position">web @ 个体</div></div></div><div data-v-6fd44370="" class="content"><!----><span data-v-6fd44370="" class="content-html">如果一方不是字符串或者数字，那么会将它转换为数字或者字符串</span><!----></div><div data-v-6fd44370="" class="footer"><span data-v-6fd44370="" class="date">11天前</span><a data-v-6fd44370="" class="reply-btn">回复</a><!----></div></div><!----></div></li><li data-v-4afc11f9="" class="item"><div data-v-6fd44370="" data-v-4afc11f9="" class="sub-comment sub-comment"><div data-v-3a6943ce="" data-v-6fd44370="" st:block="userPopover" st:state="5b38b43ee51d45589d67f498" class="user-popover-box user-popover--avatar"><!----><div data-v-57c47624="" data-v-cf310dfc="" data-v-6fd44370="" data-src="https://thirdwx.qlogo.cn/mmopen/vi_32/Q0j4TwGTfTK7DepRj94lyz4O9Fibria1cN9rJW8AKlQnLbL8brjLVgQWluDcCG0twricUAzichxcwz7vXgfIOib6R9g/132" class="lazy avatar avatar" data-v-3a6943ce="" style="background-image: none;"></div></div><div data-v-6fd44370="" class="content-box"><div data-v-6fd44370="" class="header"><div data-v-6fd44370="" class="user-info"><div data-v-3a6943ce="" data-v-6fd44370="" st:block="userPopover" st:state="5b38b43ee51d45589d67f498" class="user-popover-box user-popover--info"><!----><a data-v-6fd44370="" href="https://juejin.im/user/5b38b43ee51d45589d67f498" target="_blank" rel="" class="username" data-v-3a6943ce="">lucahan在搞GIS</a></div><div data-v-6fd44370="" class="position">低级API工程师 @ 华南光电科技公司</div></div></div><div data-v-6fd44370="" class="content"><span data-v-6fd44370="" class="text-reply">回复<a data-v-6fd44370="" href="https://juejin.im/user/5b0e60f6f265da08f0339162" target="_blank" rel=""><span data-v-6fd44370="" class="username">dsying</span></a>：</span><span data-v-6fd44370="" class="content-html">这句话我又不是没看到。我认为这句话解释不了true+true为什么等于2。true+true等于2的解释应该使用的是当boolean类型相加时，true/false会向number转换进行计算。而当boolean与非boolean进行运算时，才应该触发特点二。</span><!----></div><div data-v-6fd44370="" class="footer"><span data-v-6fd44370="" class="date">11天前</span><a data-v-6fd44370="" class="reply-btn">回复</a><!----></div></div><!----></div></li><li data-v-4afc11f9="" class="item"><div data-v-6fd44370="" data-v-4afc11f9="" class="sub-comment sub-comment"><div data-v-3a6943ce="" data-v-6fd44370="" st:block="userPopover" st:state="5bbb7e966fb9a05d0d288910" class="user-popover-box user-popover--avatar"><!----><div data-v-57c47624="" data-v-cf310dfc="" data-v-6fd44370="" data-src="https://thirdwx.qlogo.cn/mmopen/vi_32/7xBejUvOATog16y0KbrGFF25ce6ALt83EvlzGMHDeW9209sMEkIO8FZBYW7lykDJagQ3MkoHCNR8tMX2EEJx3A/132" class="lazy avatar avatar" data-v-3a6943ce="" style="background-image: none;"></div></div><div data-v-6fd44370="" class="content-box"><div data-v-6fd44370="" class="header"><div data-v-6fd44370="" class="user-info"><div data-v-3a6943ce="" data-v-6fd44370="" st:block="userPopover" st:state="5bbb7e966fb9a05d0d288910" class="user-popover-box user-popover--info"><!----><a data-v-6fd44370="" href="https://juejin.im/user/5bbb7e966fb9a05d0d288910" target="_blank" rel="" class="username" data-v-3a6943ce="">太微天帝</a></div><div data-v-6fd44370="" class="position">前端工程师 @ 博客地址：http://119.27.166.247</div></div></div><div data-v-6fd44370="" class="content"><!----><span data-v-6fd44370="" class="content-html">这么给你说吧，这里的布尔值其实也转换成数字了两个true就相当于两个1，1也也可以表示true，不信的话你可以这样试试Boolean（1）返回的也是true</span><!----></div><div data-v-6fd44370="" class="footer"><span data-v-6fd44370="" class="date">5天前</span><a data-v-6fd44370="" class="reply-btn">回复</a><!----></div></div><!----></div></li><li data-v-4afc11f9="" class="item"><div data-v-6fd44370="" data-v-4afc11f9="" class="sub-comment sub-comment"><div data-v-3a6943ce="" data-v-6fd44370="" st:block="userPopover" st:state="5acee71e5188255cb07d7e5b" class="user-popover-box user-popover--avatar"><!----><div data-v-57c47624="" data-v-cf310dfc="" data-v-6fd44370="" data-src="https://tva3.sinaimg.cn/crop.0.0.180.180.180/9ae60707jw1e8qgp5bmzyj2050050aa8.jpg" class="lazy avatar avatar" data-v-3a6943ce="" style="background-image: none;"></div></div><div data-v-6fd44370="" class="content-box"><div data-v-6fd44370="" class="header"><div data-v-6fd44370="" class="user-info"><div data-v-3a6943ce="" data-v-6fd44370="" st:block="userPopover" st:state="5acee71e5188255cb07d7e5b" class="user-popover-box user-popover--info"><!----><a data-v-6fd44370="" href="https://juejin.im/user/5acee71e5188255cb07d7e5b" target="_blank" rel="" class="username" data-v-3a6943ce="">二道思无邪</a></div><div data-v-6fd44370="" class="position">fe @ 百度</div></div></div><div data-v-6fd44370="" class="content"><!----><span data-v-6fd44370="" class="content-html">我觉得是先转原始类型的那个逻辑，先调valueOf(),返回1。
虽然true本身是原始类型，但是无法计算吧，这个我也不是很清晰</span><!----></div><div data-v-6fd44370="" class="footer"><span data-v-6fd44370="" class="date">1天前</span><a data-v-6fd44370="" class="reply-btn">回复</a><!----></div></div><!----></div></li><li data-v-4afc11f9="" class="item"><div data-v-6fd44370="" data-v-4afc11f9="" class="sub-comment sub-comment"><div data-v-3a6943ce="" data-v-6fd44370="" st:block="userPopover" st:state="5acee71e5188255cb07d7e5b" class="user-popover-box user-popover--avatar"><!----><div data-v-57c47624="" data-v-cf310dfc="" data-v-6fd44370="" data-src="https://tva3.sinaimg.cn/crop.0.0.180.180.180/9ae60707jw1e8qgp5bmzyj2050050aa8.jpg" class="lazy avatar avatar" data-v-3a6943ce="" style="background-image: none;"></div></div><div data-v-6fd44370="" class="content-box"><div data-v-6fd44370="" class="header"><div data-v-6fd44370="" class="user-info"><div data-v-3a6943ce="" data-v-6fd44370="" st:block="userPopover" st:state="5acee71e5188255cb07d7e5b" class="user-popover-box user-popover--info"><!----><a data-v-6fd44370="" href="https://juejin.im/user/5acee71e5188255cb07d7e5b" target="_blank" rel="" class="username" data-v-3a6943ce="">二道思无邪</a></div><div data-v-6fd44370="" class="position">fe @ 百度</div></div></div><div data-v-6fd44370="" class="content"><span data-v-6fd44370="" class="text-reply">回复<a data-v-6fd44370="" href="https://juejin.im/user/5acee71e5188255cb07d7e5b" target="_blank" rel=""><span data-v-6fd44370="" class="username">二道思无邪</span></a>：</span><span data-v-6fd44370="" class="content-html">我说的不对。。。普通类型要而且两个都不是字符串要先转数字</span><!----></div><div data-v-6fd44370="" class="footer"><span data-v-6fd44370="" class="date">1天前</span><a data-v-6fd44370="" class="reply-btn">回复</a><!----></div></div><!----></div></li></ul><!----></div><form data-v-4afc11f9="" class="reply-form"><textarea data-v-4afc11f9="" rows="1" maxlength="1024" placeholder="评论审核通过后显示" style="overflow: hidden; overflow-wrap: break-word; height: 35px;"></textarea><button data-v-4afc11f9="" class="reply-btn">评论</button></form></div></div></div><!----></div></li><li data-v-6adae277="" class="item"><div data-v-38783431="" data-v-6adae277="" class="comment"><div data-v-3a6943ce="" data-v-38783431="" st:block="userPopover" st:state="57700a730a2b58006a1e604b" class="user-popover-box"><!----><a data-v-38783431="" href="https://juejin.im/user/57700a730a2b58006a1e604b" target="_blank" rel="" data-v-3a6943ce=""><div data-v-57c47624="" data-v-cf310dfc="" data-v-38783431="" data-src="https://user-gold-cdn.xitu.io/2018/12/29/167f61bbbcc21375?imageView2/1/w/100/h/100/q/85/format/webp/interlace/1" class="lazy avatar avatar" style="background-image: none;"></div></a></div><div data-v-38783431="" class="content-box"><div data-v-38783431="" class="header"><div data-v-38783431="" class="user-info"><div data-v-3a6943ce="" data-v-38783431="" st:block="userPopover" st:state="57700a730a2b58006a1e604b" class="user-popover-box"><!----><a data-v-38783431="" href="https://juejin.im/user/57700a730a2b58006a1e604b" target="_blank" rel="" class="username" data-v-3a6943ce="">RedJam</a></div><div data-v-38783431="" class="position"></div></div></div><div data-v-38783431="" class="content"><!----><span data-v-38783431="" class="content-html">class是Es6中的，Es5中组合设计模式的一个语法糖</span><!----></div><div data-v-38783431="" class="footer"><button data-v-38783431="" class="like-btn"><i data-v-38783431="" class="collection-arrow-ion ion-arrow-up-b"></i><span data-v-38783431="">1</span></button><span data-v-38783431="" class="sub-comment-btn text-pointer"><span data-v-38783431="" class="title">评论</span><div data-v-38783431="" class="sub-comment--arrow" style="display: none;"></div></span><span data-v-38783431="" class="date">11天前</span><!----></div><!----></div><!----></div></li><li data-v-6adae277="" class="item"><div data-v-38783431="" data-v-6adae277="" class="comment"><div data-v-3a6943ce="" data-v-38783431="" st:block="userPopover" st:state="59f167e7f265da430d573cb9" class="user-popover-box"><!----><a data-v-38783431="" href="https://juejin.im/user/59f167e7f265da430d573cb9" target="_blank" rel="" data-v-3a6943ce=""><div data-v-57c47624="" data-v-cf310dfc="" data-v-38783431="" data-src="https://user-gold-cdn.xitu.io/2017/10/26/2c159b7e2fc6994a8512a1423a0ebb51?imageView2/1/w/100/h/100/q/85/format/webp/interlace/1" class="lazy avatar avatar" style="background-image: none;"></div></a></div><div data-v-38783431="" class="content-box"><div data-v-38783431="" class="header"><div data-v-38783431="" class="user-info"><div data-v-3a6943ce="" data-v-38783431="" st:block="userPopover" st:state="59f167e7f265da430d573cb9" class="user-popover-box"><!----><a data-v-38783431="" href="https://juejin.im/user/59f167e7f265da430d573cb9" target="_blank" rel="" class="username" data-v-3a6943ce="">大肉排小新</a></div><div data-v-38783431="" class="position">前端攻城狮</div></div></div><div data-v-38783431="" class="content"><!----><span data-v-38783431="" class="content-html">几个总结的特点都很到位呢</span><!----></div><div data-v-38783431="" class="footer"><button data-v-38783431="" class="like-btn"><i data-v-38783431="" class="collection-arrow-ion ion-arrow-up-b"></i><span data-v-38783431="">0</span></button><span data-v-38783431="" class="sub-comment-btn text-pointer"><span data-v-38783431="" class="title">评论</span><div data-v-38783431="" class="sub-comment--arrow" style="display: none;"></div></span><span data-v-38783431="" class="date">12天前</span><!----></div><!----></div><!----></div></li><li data-v-6adae277="" class="item"><div data-v-38783431="" data-v-6adae277="" class="comment"><div data-v-3a6943ce="" data-v-38783431="" st:block="userPopover" st:state="5c23281a518825697324593d" class="user-popover-box"><!----><a data-v-38783431="" href="https://juejin.im/user/5c23281a518825697324593d" target="_blank" rel="" data-v-3a6943ce=""><div data-v-57c47624="" data-v-cf310dfc="" data-v-38783431="" data-src="https://thirdwx.qlogo.cn/mmopen/vi_32/c1X1ntUoI7ZjKZrbzWZJvrJuzIZmzdXfmtITv1dqicTGIdejoIP70f8PQC6AWD2Tf5FKox8KZYiagPJmUP8UjT3g/132" class="lazy avatar avatar" style="background-image: none;"></div></a></div><div data-v-38783431="" class="content-box"><div data-v-38783431="" class="header"><div data-v-38783431="" class="user-info"><div data-v-3a6943ce="" data-v-38783431="" st:block="userPopover" st:state="5c23281a518825697324593d" class="user-popover-box"><!----><a data-v-38783431="" href="https://juejin.im/user/5c23281a518825697324593d" target="_blank" rel="" class="username" data-v-3a6943ce="">amy爱学习</a></div><div data-v-38783431="" class="position"></div></div></div><div data-v-38783431="" class="content"><!----><span data-v-38783431="" class="content-html">class PrimitiveString {
static [Symbol.hasInstance](x) {
return typeof x === 'string'
}
}
不懂这段代码，谁能讲下相关知识点？</span><!----></div><div data-v-38783431="" class="footer"><button data-v-38783431="" class="like-btn"><i data-v-38783431="" class="collection-arrow-ion ion-arrow-up-b"></i><span data-v-38783431="">0</span></button><span data-v-38783431="" class="sub-comment-btn text-pointer"><span data-v-38783431="" class="title">收起评论</span><div data-v-38783431="" class="sub-comment--arrow" style=""></div></span><span data-v-38783431="" class="date">12天前</span><!----></div><div data-v-4afc11f9="" data-v-38783431="" class="sub-comment-box sub-comment-box"><div data-v-4afc11f9="" class="sub-comment-box__top"><div data-v-4afc11f9="" class="icon-close"></div><h3 data-v-4afc11f9="">评论</h3></div><div data-v-4afc11f9="" class="sub-comment-box__inner"><div data-v-4afc11f9=""><ul data-v-4afc11f9="" class="sub-comment-list"><li data-v-4afc11f9="" class="item"><div data-v-6fd44370="" data-v-4afc11f9="" class="sub-comment sub-comment"><div data-v-3a6943ce="" data-v-6fd44370="" st:block="userPopover" st:state="598cfa26f265da3e0e1065e4" class="user-popover-box user-popover--avatar"><!----><div data-v-57c47624="" data-v-cf310dfc="" data-v-6fd44370="" data-src="https://user-gold-cdn.xitu.io/2018/7/25/164cf59ef8fbe5b4?imageView2/1/w/100/h/100/q/85/format/webp/interlace/1" class="lazy avatar avatar" data-v-3a6943ce="" style="background-image: none;"></div></div><div data-v-6fd44370="" class="content-box"><div data-v-6fd44370="" class="header"><div data-v-6fd44370="" class="user-info"><div data-v-3a6943ce="" data-v-6fd44370="" st:block="userPopover" st:state="598cfa26f265da3e0e1065e4" class="user-popover-box user-popover--info"><!----><a data-v-6fd44370="" href="https://juejin.im/user/598cfa26f265da3e0e1065e4" target="_blank" rel="" class="username" data-v-3a6943ce="">李雨冰</a></div><div data-v-6fd44370="" class="position">前端 @ MYCOMPANY</div></div></div><div data-v-6fd44370="" class="content"><!----><span data-v-6fd44370="" class="content-html">这是es6的知识，定义了一个类，然后重写了类的instanceof方法</span><!----></div><div data-v-6fd44370="" class="footer"><span data-v-6fd44370="" class="date">11天前</span><a data-v-6fd44370="" class="reply-btn">回复</a><!----></div></div><!----></div></li><li data-v-4afc11f9="" class="item"><div data-v-6fd44370="" data-v-4afc11f9="" class="sub-comment sub-comment"><div data-v-3a6943ce="" data-v-6fd44370="" st:block="userPopover" st:state="5b0e60f6f265da08f0339162" class="user-popover-box user-popover--avatar"><!----><div data-v-57c47624="" data-v-cf310dfc="" data-v-6fd44370="" data-src="https://user-gold-cdn.xitu.io/2018/8/3/164fdd0cb5708bf0?imageView2/1/w/100/h/100/q/85/format/webp/interlace/1" class="lazy avatar avatar" data-v-3a6943ce="" style="background-image: none;"></div></div><div data-v-6fd44370="" class="content-box"><div data-v-6fd44370="" class="header"><div data-v-6fd44370="" class="user-info"><div data-v-3a6943ce="" data-v-6fd44370="" st:block="userPopover" st:state="5b0e60f6f265da08f0339162" class="user-popover-box user-popover--info"><!----><a data-v-6fd44370="" href="https://juejin.im/user/5b0e60f6f265da08f0339162" target="_blank" rel="" class="username" data-v-3a6943ce="">dsying</a></div><div data-v-6fd44370="" class="position">web @ 个体</div></div></div><div data-v-6fd44370="" class="content"><!----><span data-v-6fd44370="" class="content-html">static 标记静态属性，通过 类.属性名 的方式调用</span><!----></div><div data-v-6fd44370="" class="footer"><span data-v-6fd44370="" class="date">11天前</span><a data-v-6fd44370="" class="reply-btn">回复</a><!----></div></div><!----></div></li><li data-v-4afc11f9="" class="item"><div data-v-6fd44370="" data-v-4afc11f9="" class="sub-comment sub-comment"><div data-v-3a6943ce="" data-v-6fd44370="" st:block="userPopover" st:state="59ba13fb5188256bd733c149" class="user-popover-box user-popover--avatar"><!----><div data-v-57c47624="" data-v-cf310dfc="" data-v-6fd44370="" data-src="https://wx.qlogo.cn/mmopen/vi_32/icRMfxTtOCJWk0s4OJh1WbIicmhyJt9yiayXN0vyNGsibjvrD0DQIplOneJ92IdDKv0JicRXNTnkAlu5uOibfJhdtH8Q/0" class="lazy avatar avatar" data-v-3a6943ce="" style="background-image: none;"></div></div><div data-v-6fd44370="" class="content-box"><div data-v-6fd44370="" class="header"><div data-v-6fd44370="" class="user-info"><div data-v-3a6943ce="" data-v-6fd44370="" st:block="userPopover" st:state="59ba13fb5188256bd733c149" class="user-popover-box user-popover--info"><!----><a data-v-6fd44370="" href="https://juejin.im/user/59ba13fb5188256bd733c149" target="_blank" rel="" class="username" data-v-3a6943ce="">闹闹不爱闹</a></div><div data-v-6fd44370="" class="position"></div></div></div><div data-v-6fd44370="" class="content"><!----><span data-v-6fd44370="" class="content-html">这段代码如果拿es5，静态属性怎么表达呢</span><!----></div><div data-v-6fd44370="" class="footer"><span data-v-6fd44370="" class="date">11天前</span><a data-v-6fd44370="" class="reply-btn">回复</a><!----></div></div><!----></div></li><li data-v-4afc11f9="" class="item"><div data-v-6fd44370="" data-v-4afc11f9="" class="sub-comment sub-comment"><div data-v-3a6943ce="" data-v-6fd44370="" st:block="userPopover" st:state="5b0e60f6f265da08f0339162" class="user-popover-box user-popover--avatar"><!----><div data-v-57c47624="" data-v-cf310dfc="" data-v-6fd44370="" data-src="https://user-gold-cdn.xitu.io/2018/8/3/164fdd0cb5708bf0?imageView2/1/w/100/h/100/q/85/format/webp/interlace/1" class="lazy avatar avatar" data-v-3a6943ce="" style="background-image: none;"></div></div><div data-v-6fd44370="" class="content-box"><div data-v-6fd44370="" class="header"><div data-v-6fd44370="" class="user-info"><div data-v-3a6943ce="" data-v-6fd44370="" st:block="userPopover" st:state="5b0e60f6f265da08f0339162" class="user-popover-box user-popover--info"><!----><a data-v-6fd44370="" href="https://juejin.im/user/5b0e60f6f265da08f0339162" target="_blank" rel="" class="username" data-v-3a6943ce="">dsying</a></div><div data-v-6fd44370="" class="position">web @ 个体</div></div></div><div data-v-6fd44370="" class="content"><span data-v-6fd44370="" class="text-reply">回复<a data-v-6fd44370="" href="https://juejin.im/user/59ba13fb5188256bd733c149" target="_blank" rel=""><span data-v-6fd44370="" class="username">闹闹不爱闹</span></a>：</span><span data-v-6fd44370="" class="content-html">const PrimitiveString = {}
PrimitiveString[Symbol.hasInstance] = function(x) {
return typeof x === 'string'
}</span><!----></div><div data-v-6fd44370="" class="footer"><span data-v-6fd44370="" class="date">11天前</span><a data-v-6fd44370="" class="reply-btn">回复</a><!----></div></div><!----></div></li><li data-v-4afc11f9="" class="item"><div data-v-6fd44370="" data-v-4afc11f9="" class="sub-comment sub-comment"><div data-v-3a6943ce="" data-v-6fd44370="" st:block="userPopover" st:state="5c221220e51d4574572908a0" class="user-popover-box user-popover--avatar"><!----><div data-v-57c47624="" data-v-cf310dfc="" data-v-6fd44370="" data-src="https://user-gold-cdn.xitu.io/2019/1/3/168143a54229bfe9?imageView2/1/w/100/h/100/q/85/format/webp/interlace/1" class="lazy avatar avatar" data-v-3a6943ce="" style="background-image: none;"></div></div><div data-v-6fd44370="" class="content-box"><div data-v-6fd44370="" class="header"><div data-v-6fd44370="" class="user-info"><div data-v-3a6943ce="" data-v-6fd44370="" st:block="userPopover" st:state="5c221220e51d4574572908a0" class="user-popover-box user-popover--info"><!----><a data-v-6fd44370="" href="https://juejin.im/user/5c221220e51d4574572908a0" target="_blank" rel="" class="username" data-v-3a6943ce="">Alian666</a></div><div data-v-6fd44370="" class="position"></div></div></div><div data-v-6fd44370="" class="content"><span data-v-6fd44370="" class="text-reply">回复<a data-v-6fd44370="" href="https://juejin.im/user/5b0e60f6f265da08f0339162" target="_blank" rel=""><span data-v-6fd44370="" class="username">dsying</span></a>：</span><span data-v-6fd44370="" class="content-html">假如较真一点，const也是es6的内容，如果用es5的方式，是不是还要做什么处理？</span><!----></div><div data-v-6fd44370="" class="footer"><span data-v-6fd44370="" class="date">6天前</span><a data-v-6fd44370="" class="reply-btn">回复</a><!----></div></div><!----></div></li></ul><ul data-v-5d3e9a75="" data-v-4afc11f9="" class="pagination pagination"><!----><li data-v-5d3e9a75="" class="item current">1</li><li data-v-5d3e9a75="" class="item">2</li><li data-v-5d3e9a75="" class="item">下一页</li></ul></div><form data-v-4afc11f9="" class="reply-form"><textarea data-v-4afc11f9="" rows="1" maxlength="1024" placeholder="评论审核通过后显示" style="overflow: hidden; overflow-wrap: break-word; height: 35px;"></textarea><button data-v-4afc11f9="" class="reply-btn">评论</button></form></div></div></div><!----></div></li><li data-v-6adae277="" class="item"><div data-v-38783431="" data-v-6adae277="" class="comment"><div data-v-3a6943ce="" data-v-38783431="" st:block="userPopover" st:state="5ae43778f265da0b9671fbd1" class="user-popover-box"><!----><a data-v-38783431="" href="https://juejin.im/user/5ae43778f265da0b9671fbd1" target="_blank" rel="" data-v-3a6943ce=""><div data-v-57c47624="" data-v-cf310dfc="" data-v-38783431="" data-src="https://thirdwx.qlogo.cn/mmopen/vi_32/Q0j4TwGTfTKU9KPia4VHDopo7C6EBxGTib9ibsQgQVNMacPzentx0j25T6t4QcuNX22bcJuaiahliaTjhJfc1P3lHPA/132" class="lazy avatar avatar" style="background-image: none;"></div></a></div><div data-v-38783431="" class="content-box"><div data-v-38783431="" class="header"><div data-v-38783431="" class="user-info"><div data-v-3a6943ce="" data-v-38783431="" st:block="userPopover" st:state="5ae43778f265da0b9671fbd1" class="user-popover-box"><!----><a data-v-38783431="" href="https://juejin.im/user/5ae43778f265da0b9671fbd1" target="_blank" rel="" class="username" data-v-3a6943ce="">wxy同志</a></div><div data-v-38783431="" class="position"></div></div></div><div data-v-38783431="" class="content"><!----><span data-v-38783431="" class="content-html">看起来不错呢</span><!----></div><div data-v-38783431="" class="footer"><button data-v-38783431="" class="like-btn"><i data-v-38783431="" class="collection-arrow-ion ion-arrow-up-b"></i><span data-v-38783431="">0</span></button><span data-v-38783431="" class="sub-comment-btn text-pointer"><span data-v-38783431="" class="title">评论</span><div data-v-38783431="" class="sub-comment--arrow" style="display: none;"></div></span><span data-v-38783431="" class="date">13天前</span><!----></div><!----></div><!----></div></li><li data-v-6adae277="" class="item"><div data-v-38783431="" data-v-6adae277="" class="comment"><div data-v-3a6943ce="" data-v-38783431="" st:block="userPopover" st:state="5b0e60f6f265da08f0339162" class="user-popover-box"><!----><a data-v-38783431="" href="https://juejin.im/user/5b0e60f6f265da08f0339162" target="_blank" rel="" data-v-3a6943ce=""><div data-v-57c47624="" data-v-cf310dfc="" data-v-38783431="" data-src="https://user-gold-cdn.xitu.io/2018/8/3/164fdd0cb5708bf0?imageView2/1/w/100/h/100/q/85/format/webp/interlace/1" class="lazy avatar avatar" style="background-image: none;"></div></a></div><div data-v-38783431="" class="content-box"><div data-v-38783431="" class="header"><div data-v-38783431="" class="user-info"><div data-v-3a6943ce="" data-v-38783431="" st:block="userPopover" st:state="5b0e60f6f265da08f0339162" class="user-popover-box"><!----><a data-v-38783431="" href="https://juejin.im/user/5b0e60f6f265da08f0339162" target="_blank" rel="" class="username" data-v-3a6943ce="">dsying</a></div><div data-v-38783431="" class="position">web @ 个体</div></div></div><div data-v-38783431="" class="content"><!----><span data-v-38783431="" class="content-html">```
function foo() {
console.log(this.a)
}
let a = 1
foo()
```
大佬 你这个例子 在这里 应该不符合你的意思， let 不会 绑定到window上 ，所以 this.a 是undefined</span><!----></div><div data-v-38783431="" class="footer"><button data-v-38783431="" class="like-btn"><i data-v-38783431="" class="collection-arrow-ion ion-arrow-up-b"></i><span data-v-38783431="">11</span></button><span data-v-38783431="" class="sub-comment-btn text-pointer"><span data-v-38783431="" class="title">收起评论</span><div data-v-38783431="" class="sub-comment--arrow" style=""></div></span><span data-v-38783431="" class="date">13天前</span><!----></div><div data-v-4afc11f9="" data-v-38783431="" class="sub-comment-box sub-comment-box"><div data-v-4afc11f9="" class="sub-comment-box__top"><div data-v-4afc11f9="" class="icon-close"></div><h3 data-v-4afc11f9="">评论</h3></div><div data-v-4afc11f9="" class="sub-comment-box__inner"><div data-v-4afc11f9=""><ul data-v-4afc11f9="" class="sub-comment-list"><li data-v-4afc11f9="" class="item"><div data-v-6fd44370="" data-v-4afc11f9="" class="sub-comment sub-comment"><div data-v-3a6943ce="" data-v-6fd44370="" st:block="userPopover" st:state="5c238c36e51d45463769b2fe" class="user-popover-box user-popover--avatar"><!----><div data-v-57c47624="" data-v-cf310dfc="" data-v-6fd44370="" data-src="https://thirdwx.qlogo.cn/mmopen/vi_32/Q0j4TwGTfTKRcnUicxyYKuk94n3JCAf1JickVaSibruZTOE8Cyo8YVcicenFPYjeDRzpaa7RslNMr7nE4cW4kud9og/132" class="lazy avatar avatar" data-v-3a6943ce="" style="background-image: none;"></div></div><div data-v-6fd44370="" class="content-box"><div data-v-6fd44370="" class="header"><div data-v-6fd44370="" class="user-info"><div data-v-3a6943ce="" data-v-6fd44370="" st:block="userPopover" st:state="5c238c36e51d45463769b2fe" class="user-popover-box user-popover--info"><!----><a data-v-6fd44370="" href="https://juejin.im/user/5c238c36e51d45463769b2fe" target="_blank" rel="" class="username" data-v-3a6943ce="">958</a></div><div data-v-6fd44370="" class="position"></div></div></div><div data-v-6fd44370="" class="content"><!----><span data-v-6fd44370="" class="content-html">你的a是不是没有传参进函数</span><!----></div><div data-v-6fd44370="" class="footer"><span data-v-6fd44370="" class="date">12天前</span><a data-v-6fd44370="" class="reply-btn">回复</a><!----></div></div><!----></div></li><li data-v-4afc11f9="" class="item"><div data-v-6fd44370="" data-v-4afc11f9="" class="sub-comment sub-comment"><div data-v-3a6943ce="" data-v-6fd44370="" st:block="userPopover" st:state="5b0e60f6f265da08f0339162" class="user-popover-box user-popover--avatar"><!----><div data-v-57c47624="" data-v-cf310dfc="" data-v-6fd44370="" data-src="https://user-gold-cdn.xitu.io/2018/8/3/164fdd0cb5708bf0?imageView2/1/w/100/h/100/q/85/format/webp/interlace/1" class="lazy avatar avatar" data-v-3a6943ce="" style="background-image: none;"></div></div><div data-v-6fd44370="" class="content-box"><div data-v-6fd44370="" class="header"><div data-v-6fd44370="" class="user-info"><div data-v-3a6943ce="" data-v-6fd44370="" st:block="userPopover" st:state="5b0e60f6f265da08f0339162" class="user-popover-box user-popover--info"><!----><a data-v-6fd44370="" href="https://juejin.im/user/5b0e60f6f265da08f0339162" target="_blank" rel="" class="username" data-v-3a6943ce="">dsying</a></div><div data-v-6fd44370="" class="position">web @ 个体</div></div></div><div data-v-6fd44370="" class="content"><!----><span data-v-6fd44370="" class="content-html">通过this读取window上的变量a，和传参有什么关系</span><!----></div><div data-v-6fd44370="" class="footer"><span data-v-6fd44370="" class="date">11天前</span><a data-v-6fd44370="" class="reply-btn">回复</a><!----></div></div><!----></div></li><li data-v-4afc11f9="" class="item"><div data-v-6fd44370="" data-v-4afc11f9="" class="sub-comment sub-comment"><div data-v-3a6943ce="" data-v-6fd44370="" st:block="userPopover" st:state="5af857126fb9a07ac90d4dd6" class="user-popover-box user-popover--avatar"><!----><div data-v-57c47624="" data-v-cf310dfc="" data-v-6fd44370="" data-src="https://thirdwx.qlogo.cn/mmopen/vi_32/y5eITvERZuuKShMjSUqib3t7DrRZib6EnovYlMGgmbHzpPbKqwyJW8Ey9neHLWvmiaWrJINNeJVDtSpsXv0pNyeJA/132" class="lazy avatar avatar" data-v-3a6943ce="" style="background-image: none;"></div></div><div data-v-6fd44370="" class="content-box"><div data-v-6fd44370="" class="header"><div data-v-6fd44370="" class="user-info"><div data-v-3a6943ce="" data-v-6fd44370="" st:block="userPopover" st:state="5af857126fb9a07ac90d4dd6" class="user-popover-box user-popover--info"><!----><a data-v-6fd44370="" href="https://juejin.im/user/5af857126fb9a07ac90d4dd6" target="_blank" rel="" class="username" data-v-3a6943ce="">哎呦歪</a></div><div data-v-6fd44370="" class="position">web前端开发</div></div></div><div data-v-6fd44370="" class="content"><!----><span data-v-6fd44370="" class="content-html">let 声明的变量不会挂在window上，var声明的会</span><!----></div><div data-v-6fd44370="" class="footer"><span data-v-6fd44370="" class="date">11天前</span><a data-v-6fd44370="" class="reply-btn">回复</a><!----></div></div><!----></div></li><li data-v-4afc11f9="" class="item"><div data-v-6fd44370="" data-v-4afc11f9="" class="sub-comment sub-comment"><div data-v-3a6943ce="" data-v-6fd44370="" st:block="userPopover" st:state="5be6ff3e51882516cd708de4" class="user-popover-box user-popover--avatar"><!----><div data-v-57c47624="" data-v-cf310dfc="" data-v-6fd44370="" data-src="https://avatars2.githubusercontent.com/u/38236070?v=4" class="lazy avatar avatar" data-v-3a6943ce="" style="background-image: none;"></div></div><div data-v-6fd44370="" class="content-box"><div data-v-6fd44370="" class="header"><div data-v-6fd44370="" class="user-info"><div data-v-3a6943ce="" data-v-6fd44370="" st:block="userPopover" st:state="5be6ff3e51882516cd708de4" class="user-popover-box user-popover--info"><!----><a data-v-6fd44370="" href="https://juejin.im/user/5be6ff3e51882516cd708de4" target="_blank" rel="" class="username" data-v-3a6943ce="">86driver</a></div><div data-v-6fd44370="" class="position"></div></div></div><div data-v-6fd44370="" class="content"><!----><span data-v-6fd44370="" class="content-html">大佬好眼力</span><!----></div><div data-v-6fd44370="" class="footer"><span data-v-6fd44370="" class="date">10天前</span><a data-v-6fd44370="" class="reply-btn">回复</a><!----></div></div><!----></div></li><li data-v-4afc11f9="" class="item"><div data-v-6fd44370="" data-v-4afc11f9="" class="sub-comment sub-comment"><div data-v-3a6943ce="" data-v-6fd44370="" st:block="userPopover" st:state="59de0ac151882578b8184826" class="user-popover-box user-popover--avatar"><!----><div data-v-57c47624="" data-v-cf310dfc="" data-v-6fd44370="" data-src="https://avatars0.githubusercontent.com/u/20055312?v=4" class="lazy avatar avatar" data-v-3a6943ce="" style="background-image: none;"></div></div><div data-v-6fd44370="" class="content-box"><div data-v-6fd44370="" class="header"><div data-v-6fd44370="" class="user-info"><div data-v-3a6943ce="" data-v-6fd44370="" st:block="userPopover" st:state="59de0ac151882578b8184826" class="user-popover-box user-popover--info"><!----><a data-v-6fd44370="" href="https://juejin.im/user/59de0ac151882578b8184826" target="_blank" rel="" class="username" data-v-3a6943ce="">raintao</a></div><div data-v-6fd44370="" class="position">web</div></div></div><div data-v-6fd44370="" class="content"><!----><span data-v-6fd44370="" class="content-html">let 声明的变量不会挂在window上，结果应该是undefined</span><!----></div><div data-v-6fd44370="" class="footer"><span data-v-6fd44370="" class="date">6天前</span><a data-v-6fd44370="" class="reply-btn">回复</a><!----></div></div><!----></div></li></ul><ul data-v-5d3e9a75="" data-v-4afc11f9="" class="pagination pagination"><!----><li data-v-5d3e9a75="" class="item current">1</li><li data-v-5d3e9a75="" class="item">2</li><li data-v-5d3e9a75="" class="item">下一页</li></ul></div><form data-v-4afc11f9="" class="reply-form"><textarea data-v-4afc11f9="" rows="1" maxlength="1024" placeholder="评论审核通过后显示" style="overflow: hidden; overflow-wrap: break-word; height: 35px;"></textarea><button data-v-4afc11f9="" class="reply-btn">评论</button></form></div></div></div><!----></div></li><li data-v-6adae277="" class="item"><div data-v-38783431="" data-v-6adae277="" class="comment"><div data-v-3a6943ce="" data-v-38783431="" st:block="userPopover" st:state="58758be7128fe1006b4840e8" class="user-popover-box"><!----><a data-v-38783431="" href="https://juejin.im/user/58758be7128fe1006b4840e8" target="_blank" rel="" data-v-3a6943ce=""><div data-v-57c47624="" data-v-cf310dfc="" data-v-38783431="" data-src="https://user-gold-cdn.xitu.io/2017/12/15/16055c80c2960ba3?imageView2/1/w/100/h/100/q/85/format/webp/interlace/1" class="lazy avatar avatar" style="background-image: none;"></div></a></div><div data-v-38783431="" class="content-box"><div data-v-38783431="" class="header"><div data-v-38783431="" class="user-info"><div data-v-3a6943ce="" data-v-38783431="" st:block="userPopover" st:state="58758be7128fe1006b4840e8" class="user-popover-box"><!----><a data-v-38783431="" href="https://juejin.im/user/58758be7128fe1006b4840e8" target="_blank" rel="" class="username" data-v-3a6943ce="">徐小响</a></div><div data-v-38783431="" class="position">前端开发 @ 观脉通讯</div></div></div><div data-v-38783431="" class="content"><!----><span data-v-38783431="" class="content-html">看<你不知道的JavaScript>上中下，不就行了。</span><!----></div><div data-v-38783431="" class="footer"><button data-v-38783431="" class="like-btn"><i data-v-38783431="" class="collection-arrow-ion ion-arrow-up-b"></i><span data-v-38783431="">0</span></button><span data-v-38783431="" class="sub-comment-btn text-pointer"><span data-v-38783431="" class="title">收起评论</span><div data-v-38783431="" class="sub-comment--arrow" style=""></div></span><span data-v-38783431="" class="date">13天前</span><!----></div><div data-v-4afc11f9="" data-v-38783431="" class="sub-comment-box sub-comment-box"><div data-v-4afc11f9="" class="sub-comment-box__top"><div data-v-4afc11f9="" class="icon-close"></div><h3 data-v-4afc11f9="">评论</h3></div><div data-v-4afc11f9="" class="sub-comment-box__inner"><div data-v-4afc11f9=""><ul data-v-4afc11f9="" class="sub-comment-list"><li data-v-4afc11f9="" class="item"><div data-v-6fd44370="" data-v-4afc11f9="" class="sub-comment sub-comment"><div data-v-3a6943ce="" data-v-6fd44370="" st:block="userPopover" st:state="5c2db9b06fb9a049dc025db2" class="user-popover-box user-popover--avatar"><!----><div data-v-57c47624="" data-v-cf310dfc="" data-v-6fd44370="" data-src="https://thirdwx.qlogo.cn/mmopen/vi_32/Q0j4TwGTfTKWtH9kqVLWkDE9rDw9dctZicubMCnj13keunu9HfN4ImXPx2mwHfkE7M4Uwhu8Clib4vxL9zpFMocQ/132" class="lazy avatar avatar" data-v-3a6943ce="" style="background-image: none;"></div></div><div data-v-6fd44370="" class="content-box"><div data-v-6fd44370="" class="header"><div data-v-6fd44370="" class="user-info"><div data-v-3a6943ce="" data-v-6fd44370="" st:block="userPopover" st:state="5c2db9b06fb9a049dc025db2" class="user-popover-box user-popover--info"><!----><a data-v-6fd44370="" href="https://juejin.im/user/5c2db9b06fb9a049dc025db2" target="_blank" rel="" class="username" data-v-3a6943ce="">呵呵就是我</a></div><div data-v-6fd44370="" class="position"></div></div></div><div data-v-6fd44370="" class="content"><!----><span data-v-6fd44370="" class="content-html">是需要和你争辩下小册与书籍的概念益处的不同吗？？</span><!----></div><div data-v-6fd44370="" class="footer"><span data-v-6fd44370="" class="date">4天前</span><a data-v-6fd44370="" class="reply-btn">回复</a><!----></div></div><!----></div></li></ul><!----></div><form data-v-4afc11f9="" class="reply-form"><textarea data-v-4afc11f9="" rows="1" maxlength="1024" placeholder="评论审核通过后显示" style="overflow: hidden; overflow-wrap: break-word; height: 35px;"></textarea><button data-v-4afc11f9="" class="reply-btn">评论</button></form></div></div></div><!----></div></li><li data-v-6adae277="" class="item"><div data-v-38783431="" data-v-6adae277="" class="comment"><div data-v-3a6943ce="" data-v-38783431="" st:block="userPopover" st:state="57b000947db2a2005421b5c5" class="user-popover-box"><!----><a data-v-38783431="" href="https://juejin.im/user/57b000947db2a2005421b5c5" target="_blank" rel="" data-v-3a6943ce=""><div data-v-57c47624="" data-v-cf310dfc="" data-v-38783431="" data-src="https://user-gold-cdn.xitu.io/2016/11/29/f423b7d08a277b259790198a9d61a93f?imageView2/1/w/100/h/100/q/85/format/webp/interlace/1" class="lazy avatar avatar" style="background-image: none;"></div></a></div><div data-v-38783431="" class="content-box"><div data-v-38783431="" class="header"><div data-v-38783431="" class="user-info"><div data-v-3a6943ce="" data-v-38783431="" st:block="userPopover" st:state="57b000947db2a2005421b5c5" class="user-popover-box"><!----><a data-v-38783431="" href="https://juejin.im/user/57b000947db2a2005421b5c5" target="_blank" rel="" class="username" data-v-3a6943ce="">吴楠</a></div><div data-v-38783431="" class="position"></div></div></div><div data-v-38783431="" class="content"><!----><span data-v-38783431="" class="content-html">对象类型的内存指向时候，可以顺带介绍下指针、值和堆内存、栈内存的关系</span><!----></div><div data-v-38783431="" class="footer"><button data-v-38783431="" class="like-btn"><i data-v-38783431="" class="collection-arrow-ion ion-arrow-up-b"></i><span data-v-38783431="">5</span></button><span data-v-38783431="" class="sub-comment-btn text-pointer"><span data-v-38783431="" class="title">评论</span><div data-v-38783431="" class="sub-comment--arrow" style="display: none;"></div></span><span data-v-38783431="" class="date">14天前</span><!----></div><!----></div><!----></div></li><!----></ul></section></div></div><!----><!----></div></div><div data-v-06852630="" data-v-25b273c2="" class="book-handle book-direction" style=""><div data-v-06852630="" class="step-btn step-btn--prev"><img data-v-06852630="" src="./2.JS 基础知识点及常考面试题（一）_files/prev.87ad47e.svg"></div><div data-v-06852630="" class="step-btn step-btn--next"><img data-v-06852630="" src="./2.JS 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