Add prefer-code-point rule (#1584)

configs/recommended.js

@@ -58,6 +58,7 @@ module.exports = {
 		'unicorn/prefer-array-some': 'error',
 		// TODO: Enable this by default when targeting a Node.js version that supports `Array#at`.
 		'unicorn/prefer-at': 'off',
+		'unicorn/prefer-code-point': 'error',
 		'unicorn/prefer-date-now': 'error',
 		'unicorn/prefer-default-parameters': 'error',
 		'unicorn/prefer-dom-node-append': 'error',

docs/rules/prefer-code-point.md

@@ -0,0 +1,25 @@
+# Prefer `String#codePointAt(…)` over `String#charCodeAt(…)` and `String.fromCodePoint(…)` over `String.fromCharCode(…)`
+
+Unicode is better supported in [`String#codePointAt()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/codePointAt) and [`String.fromCodePoint()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/fromCodePoint).
+
+- [Different between `String.fromCodePoint()` and `String.fromCharCode()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/fromCodePoint#compared_to_fromcharcode)
+
+## Fail
+
+```js
+const unicorn = '🦄'.charCodeAt(0).toString(16);
+```
+
+```js
+const unicorn = String.fromCharCode(0x1f984);
+```
+
+## Pass
+
+```js
+const unicorn = '🦄'.codePointAt(0).toString(16);
+```
+
+```js
+const unicorn = String.fromCodePoint(0x1f984);
+```

readme.md

@@ -90,6 +90,7 @@ Configure it in `package.json`.
 			"unicorn/prefer-array-index-of": "error",
 			"unicorn/prefer-array-some": "error",
 			"unicorn/prefer-at": "off",
+			"unicorn/prefer-code-point": "error",
 			"unicorn/prefer-date-now": "error",
 			"unicorn/prefer-default-parameters": "error",
 			"unicorn/prefer-dom-node-append": "error",
@@ -202,6 +203,7 @@ Each rule has emojis denoting:
 | [prefer-array-index-of](docs/rules/prefer-array-index-of.md) | Prefer `Array#indexOf()` over `Array#findIndex()` when looking for the index of an item. | ✅ | 🔧 | 💡 |
 | [prefer-array-some](docs/rules/prefer-array-some.md) | Prefer `.some(…)` over `.filter(…).length` check and `.find(…)`. | ✅ | 🔧 | 💡 |
 | [prefer-at](docs/rules/prefer-at.md) | Prefer `.at()` method for index access and `String#charAt()`. |  | 🔧 | 💡 |
+| [prefer-code-point](docs/rules/prefer-code-point.md) | Prefer `String#codePointAt(…)` over `String#charCodeAt(…)` and `String.fromCodePoint(…)` over `String.fromCharCode(…)`. | ✅ |  | 💡 |
 | [prefer-date-now](docs/rules/prefer-date-now.md) | Prefer `Date.now()` to get the number of milliseconds since the Unix Epoch. | ✅ | 🔧 |  |
 | [prefer-default-parameters](docs/rules/prefer-default-parameters.md) | Prefer default parameters over reassignment. | ✅ | 🔧 | 💡 |
 | [prefer-dom-node-append](docs/rules/prefer-dom-node-append.md) | Prefer `Node#append()` over `Node#appendChild()`. | ✅ | 🔧 |  |

rules/prefer-code-point.js

@@ -0,0 +1,55 @@
+'use strict';
+const {methodCallSelector} = require('./selectors/index.js');
+
+const messages = {
+	'error/charCodeAt': 'Prefer `String#codePointAt()` over `String#charCodeAt()`.',
+	'error/fromCharCode': 'Prefer `String.fromCodePoint()` over `String.fromCharCode()`.',
+	'suggestion/charCodeAt': 'Use `String#codePointAt()`.',
+	'suggestion/fromCharCode': 'Use `String.fromCodePoint()`.',
+};
+
+const cases = [
+	{
+		selector: methodCallSelector('charCodeAt'),
+		replacement: 'codePointAt',
+	},
+	{
+		selector: methodCallSelector({object: 'String', method: 'fromCharCode'}),
+		replacement: 'fromCodePoint',
+	},
+];
+
+const create = () => Object.fromEntries(
+	cases.map(({selector, replacement}) => [
+		selector,
+		node => {
+			const method = node.callee.property;
+			const methodName = method.name;
+			const fix = fixer => fixer.replaceText(method, replacement);
+
+			return {
+				node: method,
+				messageId: `error/${methodName}`,
+				suggest: [
+					{
+						messageId: `suggestion/${methodName}`,
+						fix,
+					},
+				],
+			};
+		},
+	]),
+);
+
+module.exports = {
+	create,
+	meta: {
+		type: 'suggestion',
+		docs: {
+			description: 'Prefer `String#codePointAt(…)` over `String#charCodeAt(…)` and `String.fromCodePoint(…)` over `String.fromCharCode(…)`.',
+		},
+		hasSuggestions: true,
+		schema: [],
+		messages,
+	},
+};

test/prefer-code-point.mjs

@@ -0,0 +1,35 @@
+import {getTester} from './utils/test.mjs';
+
+const {test} = getTester(import.meta);
+
+test.snapshot({
+	valid: [
+		'"🦄".codePointAt(0)',
+		'foo.charCodeAt',
+		'new foo.charCodeAt',
+		'charCodeAt(0)',
+		'foo.charCodeAt?.(0)',
+		'foo?.charCodeAt(0)',
+		'foo[charCodeAt](0)',
+		'foo["charCodeAt"](0)',
+		'foo.notCharCodeAt(0)',
+
+		'String.fromCodePoint(0x1f984)',
+		'String.fromCodePoint',
+		'new String.fromCodePoint',
+		'fromCodePoint(foo)',
+		'String.fromCodePoint?.(foo)',
+		'String?.fromCodePoint(foo)',
+		'window.String.fromCodePoint(foo)',
+		'String[fromCodePoint](foo)',
+		'String["fromCodePoint"](foo)',
+		'String.notFromCodePoint(foo)',
+		'NotString.fromCodePoint(foo)',
+	],
+	invalid: [
+		'string.charCodeAt(index)',
+		'(( (( string )).charCodeAt( ((index)), )))',
+		'String.fromCharCode( code )',
+		'(( (( String )).fromCharCode( ((code)), ) ))',
+	],
+});

test/snapshots/prefer-code-point.mjs.md

@@ -0,0 +1,61 @@
+# Snapshot report for `test/prefer-code-point.mjs`
+
+The actual snapshot is saved in `prefer-code-point.mjs.snap`.
+
+Generated by [AVA](https://avajs.dev).
+
+## Invalid #1
+      1 | string.charCodeAt(index)
+
+> Error 1/1
+
+    `␊
+    > 1 | string.charCodeAt(index)␊
+        |        ^^^^^^^^^^ Prefer \`String#codePointAt()\` over \`String#charCodeAt()\`.␊
+    ␊
+    --------------------------------------------------------------------------------␊
+    Suggestion 1/1: Use \`String#codePointAt()\`.␊
+      1 | string.codePointAt(index)␊
+    `
+
+## Invalid #2
+      1 | (( (( string )).charCodeAt( ((index)), )))
+
+> Error 1/1
+
+    `␊
+    > 1 | (( (( string )).charCodeAt( ((index)), )))␊
+        |                 ^^^^^^^^^^ Prefer \`String#codePointAt()\` over \`String#charCodeAt()\`.␊
+    ␊
+    --------------------------------------------------------------------------------␊
+    Suggestion 1/1: Use \`String#codePointAt()\`.␊
+      1 | (( (( string )).codePointAt( ((index)), )))␊
+    `
+
+## Invalid #3
+      1 | String.fromCharCode( code )
+
+> Error 1/1
+
+    `␊
+    > 1 | String.fromCharCode( code )␊
+        |        ^^^^^^^^^^^^ Prefer \`String.fromCodePoint()\` over \`String.fromCharCode()\`.␊
+    ␊
+    --------------------------------------------------------------------------------␊
+    Suggestion 1/1: Use \`String.fromCodePoint()\`.␊
+      1 | String.fromCodePoint( code )␊
+    `
+
+## Invalid #4
+      1 | (( (( String )).fromCharCode( ((code)), ) ))
+
+> Error 1/1
+
+    `␊
+    > 1 | (( (( String )).fromCharCode( ((code)), ) ))␊
+        |                 ^^^^^^^^^^^^ Prefer \`String.fromCodePoint()\` over \`String.fromCharCode()\`.␊
+    ␊
+    --------------------------------------------------------------------------------␊
+    Suggestion 1/1: Use \`String.fromCodePoint()\`.␊
+      1 | (( (( String )).fromCodePoint( ((code)), ) ))␊
+    `