From a9aafc606225af721648b278c3e01864fd537537 Mon Sep 17 00:00:00 2001
From: Jason Williscroft <me@karmanivero.us>
Date: Fri, 26 Jul 2024 11:24:10 +0800
Subject: [PATCH] added throwif block

---
 README.md              |  8 ++++++++
 eslint.config.js       |  1 +
 src/Handlebars.test.ts | 14 ++++++++++++++
 src/Handlebars.ts      | 17 +++++++++++++++++
 4 files changed, 40 insertions(+)

diff --git a/README.md b/README.md
index 7053f4e..3ef4eef 100644
--- a/README.md
+++ b/README.md
@@ -150,3 +150,11 @@ These targets are currently available:
 | `target` | Description                                                                                     | default `delimiter` |
 | -------- | ----------------------------------------------------------------------------------------------- | ------------------- |
 | `s3`     | [S3 bucket names](https://docs.aws.amazon.com/AmazonS3/latest/userguide/bucketnamingrules.html) | `'-'`               |
+
+## throwif
+
+Checks an condition. If true, throws an error before evauating the block content. Syntax:
+
+```handlebars
+{{#throwif <condition> <message>}}No Error!{{/throwif}}
+```
diff --git a/eslint.config.js b/eslint.config.js
index 0892b72..b835ecb 100644
--- a/eslint.config.js
+++ b/eslint.config.js
@@ -25,6 +25,7 @@ export default tseslint.config(
       tsdoc: tsDocPlugin,
     },
     rules: {
+      '@typescript-eslint/no-non-null-assertion': 'off',
       '@typescript-eslint/no-unused-vars': 'error',
       'mocha/no-skipped-tests': 'off',
       'mocha/no-top-level-hooks': 'off',
diff --git a/src/Handlebars.test.ts b/src/Handlebars.test.ts
index 281645c..48657ef 100644
--- a/src/Handlebars.test.ts
+++ b/src/Handlebars.test.ts
@@ -141,4 +141,18 @@ describe('Handlebars', function () {
 
     expect(result).to.equal('metastructure-001-shared-services-s3-access-log');
   });
+
+  it('throwif true', function () {
+    const template = '{{#throwif amount "Error!"}}No Error!{{/throwif}}';
+
+    expect(() => Handlebars.compile(template)(data)).to.throw('Error!');
+  });
+
+  it('throwif false', function () {
+    const template = '{{#throwif falsy "Error!"}}No Error!{{/throwif}}';
+
+    const result = Handlebars.compile(template)(data);
+
+    expect(result).to.equal('No Error!');
+  });
 });
diff --git a/src/Handlebars.ts b/src/Handlebars.ts
index cf8c1cc..041178f 100644
--- a/src/Handlebars.ts
+++ b/src/Handlebars.ts
@@ -117,4 +117,21 @@ Handlebars.registerHelper(
   },
 );
 
+Handlebars.registerHelper(
+  'throwif',
+  function (
+    condition: boolean,
+    messageParam: string | Handlebars.HelperOptions,
+    optionsParam?: Handlebars.HelperOptions,
+  ) {
+    const message = _.isString(messageParam) ? messageParam : undefined;
+    const options = (_.isString(messageParam) ? optionsParam : messageParam)!;
+
+    if (condition) throw new Error(message);
+
+    // @ts-expect-error 'this' implicitly has type 'any' because it does not have a type annotation.
+    return options.fn(this);
+  },
+);
+
 export { Handlebars };