Add prefer-module rule (#1141)

Co-authored-by: Sindre Sorhus <sindresorhus@gmail.com>

docs/rules/prefer-module.md

@@ -0,0 +1,117 @@
+# Prefer JavaScript modules (ESM) over CommonJS
+
+Prefer using the [JavaScript module](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Modules) format over the legacy CommonJS module format.
+
+1. Forbids `'use strict'` directive.
+
+	JavaScript modules use “Strict Mode” by default.
+
+1. Forbids “Global Return”.
+
+	This is a CommonJS-only feature.
+
+1. Forbids the global variables `__dirname` and `__filename`.
+
+	They are [not available in JavaScript modules](https://nodejs.org/api/esm.html#esm_no_filename_or_dirname).
+
+	Replacements:
+
+	```js
+	import {fileURLToPath} from 'url';
+	import path from 'path';
+
+	const __filename = fileURLToPath(import.meta.url);
+	const __dirname = path.dirname(fileURLToPath(import.meta.url));
+	```
+
+	However, in most cases, this is better:
+
+	```js
+	import {fileURLToPath} from 'url';
+
+	const foo = fileURLToPath(new URL('foo.js', import.meta.url));
+	```
+
+	And many Node.js APIs accept `URL` directly, so you can just do this:
+
+	```js
+	const foo = new URL('foo.js', import.meta.url);
+	```
+
+1. Forbids `require(…)`.
+
+	`require(…)` can be replaced by `import …` or `import(…)`.
+
+1. Forbids `exports` and `module.exports`.
+
+	`export …` should be used in JavaScript modules.
+
+## Fail
+
+```js
+'use strict';
+
+// …
+```
+
+```js
+if (foo) {
+	return;
+}
+
+// …
+```
+
+```js
+const file = path.join(__dirname, 'foo.js');
+```
+
+```js
+const content = fs.readFileSync(__filename, 'utf8');
+```
+
+```js
+const {fromPairs} = require('lodash');
+```
+
+```js
+module.exports = foo;
+```
+
+```js
+exports.foo = foo;
+```
+
+## Pass
+
+```js
+function run() {
+	if (foo) {
+		return;
+	}
+
+	// …
+}
+
+run();
+```
+
+```js
+const file = fileURLToPath(new URL('foo.js', import.meta.url));
+```
+
+```js
+import {fromPairs} from 'lodash-es';
+```
+
+```js
+export default foo;
+```
+
+```js
+export {foo};
+```
+
+## Resources
+
+- [Get Ready For ESM](https://blog.sindresorhus.com/get-ready-for-esm-aa53530b3f77) by @sindresorhus

index.js

@@ -99,6 +99,7 @@ module.exports = {
 				'unicorn/prefer-keyboard-event-key': 'error',
 				'unicorn/prefer-math-trunc': 'error',
 				'unicorn/prefer-modern-dom-apis': 'error',
+				'unicorn/prefer-module': 'error',
 				'unicorn/prefer-negative-index': 'error',
 				'unicorn/prefer-number-properties': 'error',
 				'unicorn/prefer-optional-catch-binding': 'error',

readme.md

@@ -90,6 +90,7 @@ Configure it in `package.json`.
 			"unicorn/prefer-keyboard-event-key": "error",
 			"unicorn/prefer-math-trunc": "error",
 			"unicorn/prefer-modern-dom-apis": "error",
+			"unicorn/prefer-module": "error",
 			"unicorn/prefer-negative-index": "error",
 			"unicorn/prefer-number-properties": "error",
 			"unicorn/prefer-optional-catch-binding": "error",
@@ -181,6 +182,7 @@ Each rule has emojis denoting:
 | [prefer-keyboard-event-key](docs/rules/prefer-keyboard-event-key.md) | Prefer `KeyboardEvent#key` over `KeyboardEvent#keyCode`. | ✅ | 🔧 |
 | [prefer-math-trunc](docs/rules/prefer-math-trunc.md) | Enforce the use of `Math.trunc` instead of bitwise operators. | ✅ | 🔧 |
 | [prefer-modern-dom-apis](docs/rules/prefer-modern-dom-apis.md) | Prefer `.before()` over `.insertBefore()`, `.replaceWith()` over `.replaceChild()`, prefer one of `.before()`, `.after()`, `.append()` or `.prepend()` over `insertAdjacentText()` and `insertAdjacentElement()`. | ✅ | 🔧 |
+| [prefer-module](docs/rules/prefer-module.md) | Prefer JavaScript modules (ESM) over CommonJS. | ✅ | 🔧 |
 | [prefer-negative-index](docs/rules/prefer-negative-index.md) | Prefer negative index over `.length - index` for `{String,Array,TypedArray}#slice()` and `Array#splice()`. | ✅ | 🔧 |
 | [prefer-number-properties](docs/rules/prefer-number-properties.md) | Prefer `Number` static properties over global ones. | ✅ | 🔧 |
 | [prefer-optional-catch-binding](docs/rules/prefer-optional-catch-binding.md) | Prefer omitting the `catch` binding parameter. | ✅ | 🔧 |