object.md

Object

• Object.keys|values|entries
• Seal an object
• Shallow copy and deep copy an object

object-keys-values-entries

const x = {a: 1, b: 2};

Object.keys(x); // [a, b]
Object.values(x); // [1, 2]
Object.entries(x); // [['a', 1], ['b', 2]]

for (let [k, v] of Object.entries(x)) {
  console.log(`key: ${key} value: ${value}`);
}

Seal an object

Seal a object will:

• prevent new properties from being added
• marking all properties as non-configurable
• properties value can still be changed as long as they are writable.

var obj = {
  prop: function() {},
  foo: 'bar'
};

var o = Object.seal(obj);

o === obj; // true
Object.isSealed(obj); // === true

// Changing property values on a sealed object
// still works.
obj.foo = 'quux';

// But you can't convert data properties to accessors,
// or vice versa.
Object.defineProperty(obj, 'foo', {
  get: function() { return 'g'; }
}); // throws a TypeError

Object deep copy and shallow copy

Consider approaches below:

const s1 = {
  a: 12,
  b: {
    val: 'this is good'
  }
};

const s2 = Object.assign({}, s1);
const s3 = {...s1, c: 50};

Both cases DO NOT deeply clone object s1 meaning changes to b.val in s1 will also be reflected in s2 and s3. Even if primitive-typed prop a does.

To correctly clone object, use lodash.deepClone.