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feat(eslint-plugin): add new rule no-for-in-array#155
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5ff29cd feat(eslint-plugin): add new rule no-for-in-array
7d9991e chore(eslint-plugin): remove unnecessary typedefs
a333448 chore: fix README spacing
767a62f Merge branch 'master' into noForIn
j-f156fa66e Update roadmap
j-f1d532334 fix: respond to review
7582ab0 Merge branch 'master' into noForIn
uniqueiniquity64906c1 Merge branch 'master' into noForIn
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1 change: 1 addition & 0 deletionspackages/eslint-plugin/README.md
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12 changes: 9 additions & 3 deletionspackages/eslint-plugin/ROADMAP.md
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44 changes: 44 additions & 0 deletionspackages/eslint-plugin/docs/rules/no-for-in-array.md
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,44 @@ | ||
| # Disallow iterating over an array with a for-in loop (no-for-in-array) | ||
| This rule prohibits iterating over an array with a for-in loop. | ||
| ## Rule Details | ||
| Rationale from TSLint: | ||
| A for-in loop (`for (var k in o)`) iterates over the properties of an Object. | ||
| While it is legal to use for-in loops with array types, it is not common. | ||
| for-in will iterate over the indices of the array as strings, omitting any "holes" in | ||
| the array. | ||
| More common is to use for-of, which iterates over the values of an array. | ||
| If you want to iterate over the indices, alternatives include: | ||
| ```js | ||
| array.forEach((value, index) => { ... }); | ||
| for (const [index, value] of array.entries()) { ... } | ||
| for (let i = 0; i < array.length; i++) { ... } | ||
| ``` | ||
| Examples of **incorrect** code for this rule: | ||
| ```js | ||
| for (const x in [3, 4, 5]) { | ||
| console.log(x); | ||
| } | ||
| ``` | ||
| Examples of **correct** code for this rule: | ||
| ```js | ||
| for (const x in { a: 3, b: 4, c: 5 }) { | ||
| console.log(x); | ||
| } | ||
| ``` | ||
| ## When Not To Use It | ||
| If you want to iterate through a loop using the indices in an array as strings, you can turn off this rule. | ||
| ## Related to | ||
| - TSLint: ['no-for-in-array'](https://palantir.github.io/tslint/rules/no-for-in-array/) |
56 changes: 56 additions & 0 deletionspackages/eslint-plugin/lib/rules/no-for-in-array.js
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,56 @@ | ||
| /** | ||
| * @fileoverview Disallow iterating over an array with a for-in loop | ||
| * @author Benjamin Lichtman | ||
| */ | ||
| 'use strict'; | ||
| const ts = require('typescript'); | ||
| const util = require('../util'); | ||
| //------------------------------------------------------------------------------ | ||
| // Rule Definition | ||
| //------------------------------------------------------------------------------ | ||
| /** | ||
| * @type {import("eslint").Rule.RuleModule} | ||
| */ | ||
| module.exports = { | ||
| meta: { | ||
| docs: { | ||
| description: 'Disallow iterating over an array with a for-in loop', | ||
| category: 'Functionality', | ||
| recommended: false, | ||
| extraDescription: [util.tslintRule('no-for-in-array')], | ||
| url: util.metaDocsUrl('no-for-in-array') | ||
| }, | ||
| fixable: null, | ||
| messages: { | ||
| forInViolation: | ||
| 'For-in loops over arrays are forbidden. Use for-of or array.forEach instead.' | ||
| }, | ||
| schema: [], | ||
| type: 'problem' | ||
| }, | ||
| create(context) { | ||
| return { | ||
| ForInStatement(node) { | ||
| const parserServices = util.getParserServices(context); | ||
| const checker = parserServices.program.getTypeChecker(); | ||
| const originalNode = parserServices.esTreeNodeToTSNodeMap.get(node); | ||
| const type = checker.getTypeAtLocation(originalNode.expression); | ||
| if ( | ||
| (typeof type.symbol !== 'undefined' && | ||
| type.symbol.name === 'Array') || | ||
| (type.flags & ts.TypeFlags.StringLike) !== 0 | ||
| ) { | ||
| context.report({ | ||
| node, | ||
| messageId: 'forInViolation' | ||
| }); | ||
| } | ||
| } | ||
| }; | ||
| } | ||
| }; |
2 changes: 1 addition & 1 deletionpackages/eslint-plugin/lib/util.js
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69 changes: 69 additions & 0 deletionspackages/eslint-plugin/tests/lib/rules/no-for-in-array.js
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,69 @@ | ||
| /** | ||
| * @fileoverview Disallow iterating over an array with a for-in loop | ||
| * @author Benjamin Lichtman | ||
| */ | ||
| 'use strict'; | ||
| //------------------------------------------------------------------------------ | ||
| // Requirements | ||
| //------------------------------------------------------------------------------ | ||
| const rule = require('../../../lib/rules/no-for-in-array'), | ||
| RuleTester = require('eslint').RuleTester, | ||
| path = require('path'); | ||
| //------------------------------------------------------------------------------ | ||
| // Tests | ||
| //------------------------------------------------------------------------------ | ||
| const rootDir = path.join(process.cwd(), 'tests/fixtures/'); | ||
| const parserOptions = { | ||
| ecmaVersion: 2015, | ||
| tsconfigRootDir: rootDir, | ||
| project: './tsconfig.json' | ||
| }; | ||
| const ruleTester = new RuleTester({ | ||
| parserOptions, | ||
| parser: '@typescript-eslint/parser' | ||
| }); | ||
| ruleTester.run('no-for-in-array', rule, { | ||
| valid: [ | ||
| ` | ||
| for (const x of [3, 4, 5]) { | ||
| console.log(x); | ||
| }`, | ||
| ` | ||
| for (const x in { a: 1, b: 2, c: 3 }) { | ||
| console.log(x); | ||
| }` | ||
| ], | ||
| invalid: [ | ||
| { | ||
| code: ` | ||
| for (const x in [3, 4, 5]) { | ||
| console.log(x); | ||
| }`, | ||
| errors: [ | ||
| { | ||
| messageId: 'forInViolation', | ||
| type: 'ForInStatement' | ||
| } | ||
| ] | ||
| }, | ||
| { | ||
| code: ` | ||
| const z = [3, 4, 5]; | ||
| for (const x in z) { | ||
| console.log(x); | ||
| }`, | ||
| errors: [ | ||
| { | ||
| messageId: 'forInViolation', | ||
| type: 'ForInStatement' | ||
| } | ||
| ] | ||
| } | ||
| ] | ||
| }); |
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