Add prefer-at rule

docs/rules/prefer-at.md

@@ -0,0 +1,17 @@
+# Prefer `.at()` method for negative index access.
+
+<!-- More detailed description. Remove this comment. -->
+
+This rule is fixable.
+
+## Fail
+
+```js
+const foo = 'unicorn';
+```
+
+## Pass
+
+```js
+const foo = '🦄';
+```

index.js

@@ -86,6 +86,7 @@ module.exports = {
 				'unicorn/prefer-array-flat-map': 'error',
 				'unicorn/prefer-array-index-of': 'error',
 				'unicorn/prefer-array-some': 'error',
+				'unicorn/prefer-at': 'error',
 				'unicorn/prefer-date-now': 'error',
 				'unicorn/prefer-default-parameters': 'error',
 				'unicorn/prefer-dom-node-append': 'error',

readme.md

@@ -82,6 +82,7 @@ Configure it in `package.json`.
 			"unicorn/prefer-array-flat-map": "error",
 			"unicorn/prefer-array-index-of": "error",
 			"unicorn/prefer-array-some": "error",
+			"unicorn/prefer-at": "error",
 			"unicorn/prefer-date-now": "error",
 			"unicorn/prefer-default-parameters": "error",
 			"unicorn/prefer-dom-node-append": "error",
@@ -176,6 +177,7 @@ Each rule has emojis denoting:
 | [prefer-array-flat-map](docs/rules/prefer-array-flat-map.md) | Prefer `.flatMap(…)` over `.map(…).flat()`. | ✅ | 🔧 |
 | [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 `.find(…)`. | ✅ |  |
+| [prefer-at](docs/rules/prefer-at.md) | Prefer `.at()` method for negative index access. | ✅ | 🔧 |
 | [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-at.js

@@ -0,0 +1,71 @@
+'use strict';
+const {getStaticValue} = require('eslint-utils');
+const getDocumentationUrl = require('./utils/get-documentation-url');
+const isSameReference = require('./utils/is-same-reference');
+const replaceNodeOrTokenAndSpacesBefore = require('./utils/replace-node-or-token-and-spaces-before');
+
+const MESSAGE_ID = 'prefer-at';
+const messages = {
+	[MESSAGE_ID]: 'Prefer `.at()` method for negative index access.'
+};
+
+const selector = [
+	'MemberExpression',
+	'[optional!=true]',
+	'[computed=true]',
+	'[property.type="BinaryExpression"]',
+	'[property.operator="-"]',
+	'[property.left.type="MemberExpression"]',
+	'[property.left.optional!=true]',
+	'[property.left.computed=false]',
+	'[property.left.property.type="Identifier"]',
+	'[property.left.property.name="length"]'
+].join('')
+
+/** @param {import('eslint').Rule.RuleContext} context */
+const create = context => {
+	return {
+		[selector](node) {
+			const array = node.object;
+			const lengthObject = node.property.left.object;
+			if (!isSameReference(array, lengthObject)) {
+				return;
+			}
+
+			const offset = node.property.right;
+			const staticResult = getStaticValue(offset, context.getScope());
+			if (
+				!staticResult ||
+				!Number.isInteger(staticResult.value) ||
+				staticResult.value < 1
+			) {
+				return;
+			}
+
+			context.report({
+				node: node.property,
+				messageId: MESSAGE_ID,
+				/** @param {import('eslint').Rule.RuleFixer} fixer */
+				* fix(fixer) {
+					yield * replaceNodeOrTokenAndSpacesBefore(node.property.left, '', fixer, context.getSourceCode());
+				}
+			});
+		}
+	}
+};
+
+const schema = [];
+
+module.exports = {
+	create,
+	meta: {
+		type: 'suggestion',
+		docs: {
+			description: 'Prefer `.at()` method for negative index access.',
+			url: getDocumentationUrl(__filename)
+		},
+		fixable: 'code',
+		schema,
+		messages
+	}
+};

test/prefer-at.mjs

@@ -0,0 +1,31 @@
+import outdent from 'outdent';
+import {getTester} from './utils/test.mjs';
+
+const {test} = getTester(import.meta);
+
+
+test.snapshot({
+	valid: [
+		'array.at(-1)',
+		'array.at(1)',
+		'array[0]',
+		'array.foo',
+		'array[-1]',
+		'array[array.length + 1]',
+		'array[array.length - 0]',
+		'array[-10 + array.length]',
+		'array[array.length - 1n]',
+		'array[+array.length - 1]',
+		'array[array.length - -1]',
+		'array[array.length - foo]',
+		'array[array.length + -10]',
+		'const OFFSET = -1; array[array.length + OFFSET];'
+	],
+	invalid: [
+		'array[array.length - 1]',
+		'array[array.length - 10]',
+		'array[ /**/ (( /**/ (( /**/ array.length /**/ )) /**/ - /**/ (( /**/ 10 /**/ )) /**/ )) /**/ ]',
+		'const OFFSET = 1; array[array.length - OFFSET];',
+		// 'array.at(array.length - 1)'
+	]
+});

test/snapshots/prefer-at.mjs.md

@@ -0,0 +1,69 @@
+# Snapshot report for `test/prefer-at.mjs`
+
+The actual snapshot is saved in `prefer-at.mjs.snap`.
+
+Generated by [AVA](https://avajs.dev).
+
+## Invalid #1
+      1 | array[array.length - 1]
+
+> Output
+
+    `␊
+      1 | array[ - 1]␊
+    `
+
+> Error 1/1
+
+    `␊
+    > 1 | array[array.length - 1]␊
+        |       ^^^^^^^^^^^^^^^^ Prefer \`.at()\` method for negative index access.␊
+    `
+
+## Invalid #2
+      1 | array[array.length - 10]
+
+> Output
+
+    `␊
+      1 | array[ - 10]␊
+    `
+
+> Error 1/1
+
+    `␊
+    > 1 | array[array.length - 10]␊
+        |       ^^^^^^^^^^^^^^^^^ Prefer \`.at()\` method for negative index access.␊
+    `
+
+## Invalid #3
+      1 | array[ /**/ (( /**/ (( /**/ array.length /**/ )) /**/ - /**/ (( /**/ 10 /**/ )) /**/ )) /**/ ]
+
+> Output
+
+    `␊
+      1 | array[ /**/ (( /**/ /**/ /**/ /**/ - /**/ (( /**/ 10 /**/ )) /**/ )) /**/ ]␊
+    `
+
+> Error 1/1
+
+    `␊
+    > 1 | array[ /**/ (( /**/ (( /**/ array.length /**/ )) /**/ - /**/ (( /**/ 10 /**/ )) /**/ )) /**/ ]␊
+        |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Prefer \`.at()\` method for negative index access.␊
+    `
+
+## Invalid #4
+      1 | const OFFSET = 1; array[array.length - OFFSET];
+
+> Output
+
+    `␊
+      1 | const OFFSET = 1; array[ - OFFSET];␊
+    `
+
+> Error 1/1
+
+    `␊
+    > 1 | const OFFSET = 1; array[array.length - OFFSET];␊
+        |                         ^^^^^^^^^^^^^^^^^^^^^ Prefer \`.at()\` method for negative index access.␊
+    `