Add prefer-blob-reading-methods rule (#2065)

Co-authored-by: fisker <[email protected]>
sindresorhus · Apr 17, 2023 · 2bb1a04 · 2bb1a04
1 parent d90f337
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diff --git a/configs/recommended.js b/configs/recommended.js
@@ -75,6 +75,7 @@ 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-blob-reading-methods': 'error',
 		'unicorn/prefer-code-point': 'error',
 		'unicorn/prefer-date-now': 'error',
 		'unicorn/prefer-default-parameters': 'error',

diff --git a/docs/rules/prefer-blob-reading-methods.md b/docs/rules/prefer-blob-reading-methods.md
@@ -0,0 +1,45 @@
+# Prefer `Blob#arrayBuffer()` over `FileReader#readAsArrayBuffer(…)` and `Blob#text()` over `FileReader#readAsText(…)`
+
+💼 This rule is enabled in the ✅ `recommended` [config](https://github.com/sindresorhus/eslint-plugin-unicorn#preset-configs).
+
+<!-- end auto-generated rule header -->
+<!-- Do not manually modify this header. Run: `npm run fix:eslint-docs` -->
+
+`FileReader` predates promises, and the newer [`Blob#arrayBuffer()`](https://developer.mozilla.org/en-US/docs/Web/API/Blob/arrayBuffer) and [`Blob#text()`](https://developer.mozilla.org/en-US/docs/Web/API/Blob/text) methods are much cleaner and easier to use.
+
+## Fail
+
+```js
+const arrayBuffer = await new Promise((resolve, reject) => {
+	const fileReader = new FileReader();
+	fileReader.addEventListener('load', () => {
+		resolve(fileReader.result);
+	});
+	fileReader.addEventListener('error', () => {
+		reject(fileReader.error);
+	});
+	fileReader.readAsArrayBuffer(blob);
+});
+```
+
+```js
+fileReader.readAsText(blob);
+```
+
+## Pass
+
+```js
+const arrayBuffer = await blob.arrayBuffer();
+```
+
+```js
+const text = await blob.text();
+```
+
+```js
+fileReader.readAsText(blob, 'ascii');
+```
+
+```js
+fileReader.readAsDataURL(blob);
+```
diff --git a/readme.md b/readme.md
@@ -116,6 +116,7 @@ If you don't use the preset, ensure you use the same `env` and `parserOptions` c
 | [prefer-array-index-of](docs/rules/prefer-array-index-of.md)                                     | Prefer `Array#{indexOf,lastIndexOf}()` over `Array#{findIndex,findLastIndex}()` 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,findLast}(…)`.                                                                                                                                       | ✅  | 🔧 | 💡 |
 | [prefer-at](docs/rules/prefer-at.md)                                                             | Prefer `.at()` method for index access and `String#charAt()`.                                                                                                                                                     |    | 🔧 | 💡 |
+| [prefer-blob-reading-methods](docs/rules/prefer-blob-reading-methods.md)                         | Prefer `Blob#arrayBuffer()` over `FileReader#readAsArrayBuffer(…)` and `Blob#text()` over `FileReader#readAsText(…)`.                                                                                             | ✅  |    |    |
 | [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.                                                                                                                                                                      | ✅  | 🔧 | 💡 |

diff --git a/rules/prefer-blob-reading-methods.js b/rules/prefer-blob-reading-methods.js
@@ -0,0 +1,37 @@
+'use strict';
+const {methodCallSelector} = require('./selectors/index.js');
+
+const messages = {
+	'error/readAsArrayBuffer': 'Prefer `Blob#arrayBuffer()` over `FileReader#readAsArrayBuffer(blob)`.',
+	'error/readAsText': 'Prefer `Blob#text()` over `FileReader#readAsText(blob)`.',
+};
+
+const selector = methodCallSelector({
+	methods: ['readAsText', 'readAsArrayBuffer'],
+	argumentsLength: 1,
+});
+
+/** @param {import('eslint').Rule.RuleContext} context */
+const create = () => ({
+	[selector](node) {
+		const method = node.callee.property;
+		const methodName = method.name;
+
+		return {
+			node: method,
+			messageId: `error/${methodName}`,
+		};
+	},
+});
+
+/** @type {import('eslint').Rule.RuleModule} */
+module.exports = {
+	create,
+	meta: {
+		type: 'suggestion',
+		docs: {
+			description: 'Prefer `Blob#arrayBuffer()` over `FileReader#readAsArrayBuffer(…)` and `Blob#text()` over `FileReader#readAsText(…)`.',
+		},
+		messages,
+	},
+};
diff --git a/test/prefer-blob-reading-methods.mjs b/test/prefer-blob-reading-methods.mjs
@@ -0,0 +1,19 @@
+import {getTester} from './utils/test.mjs';
+
+const {test} = getTester(import.meta);
+
+test.snapshot({
+	valid: [
+		'blob.arrayBuffer()',
+		'blob.text()',
+		'new Response(blob).arrayBuffer()',
+		'new Response(blob).text()',
+		'fileReader.readAsDataURL(blob)',
+		'fileReader.readAsBinaryString(blob)',
+		'fileReader.readAsText(blob, "ascii")',
+	],
+	invalid: [
+		'fileReader.readAsArrayBuffer(blob)',
+		'fileReader.readAsText(blob)',
+	],
+});
diff --git a/test/snapshots/prefer-blob-reading-methods.mjs.md b/test/snapshots/prefer-blob-reading-methods.mjs.md
@@ -0,0 +1,25 @@
+# Snapshot report for `test/prefer-blob-reading-methods.mjs`
+
+The actual snapshot is saved in `prefer-blob-reading-methods.mjs.snap`.
+
+Generated by [AVA](https://avajs.dev).
+
+## Invalid #1
+      1 | fileReader.readAsArrayBuffer(blob)
+
+> Error 1/1
+
+    `␊
+    > 1 | fileReader.readAsArrayBuffer(blob)␊
+        |            ^^^^^^^^^^^^^^^^^ Prefer \`Blob#arrayBuffer()\` over \`FileReader#readAsArrayBuffer(blob)\`.␊
+    `
+
+## Invalid #2
+      1 | fileReader.readAsText(blob)
+
+> Error 1/1
+
+    `␊
+    > 1 | fileReader.readAsText(blob)␊
+        |            ^^^^^^^^^^ Prefer \`Blob#text()\` over \`FileReader#readAsText(blob)\`.␊
+    `
diff --git a/test/snapshots/prefer-blob-reading-methods.mjs.snap b/test/snapshots/prefer-blob-reading-methods.mjs.snap