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61 lines
1.3 KiB
Text
61 lines
1.3 KiB
Text
---
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description: 'Disallow iterating over an array with a for-in loop.'
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---
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> 🛑 This file is source code, not the primary documentation location! 🛑
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>
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> See **https://typescript-eslint.io/rules/no-for-in-array** for documentation.
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This rule prohibits iterating over an array with a for-in loop.
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## Rule Details
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A for-in loop (`for (var k in o)`) iterates over the properties of an Object.
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While it is legal to use for-in loops with array types, it is not common.
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for-in will iterate over the indices of the array as strings, omitting any "holes" in
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the array.
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More common is to use for-of, which iterates over the values of an array.
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If you want to iterate over the indices, alternatives include:
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```js
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array.forEach((value, index) => { ... });
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for (const [index, value] of array.entries()) { ... }
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for (let i = 0; i < array.length; i++) { ... }
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```
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Examples of code for this rule:
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<!--tabs-->
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### ❌ Incorrect
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```js
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for (const x in [3, 4, 5]) {
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console.log(x);
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}
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```
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### ✅ Correct
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```js
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for (const x in { a: 3, b: 4, c: 5 }) {
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console.log(x);
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}
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```
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## Options
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```jsonc
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// .eslintrc.json
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{
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"rules": {
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"@typescript-eslint/no-for-in-array": "error"
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}
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}
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```
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This rule is not configurable.
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## When Not To Use It
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If you want to iterate through a loop using the indices in an array as strings, you can turn off this rule.
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