useForOf

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JavaScript (and super languages)

Summary

Rule available since: v1.5.0
Diagnostic Category: lint/style/useForOf
This rule isn’t recommended, so you need to enable it.
This rule doesn’t have a fix.
The default severity of this rule is information.
Sources:
- Same as @typescript-eslint/prefer-for-of
- Same as unicorn/no-for-loop

How to configure

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{
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  "linter": {
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    "rules": {
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      "style": {
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        "useForOf": "error"
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      }
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    }
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  }
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}

Description

Prefer using for...of loops over standard for loops where possible.

This rule recommends using a for...of loop in place of a for loop when the loop index is solely used to read from the iterated array.

Exceptions for Index Usage

When the loop index is declared within the outer scope or used anywhere within the loop body, it is acceptable to use a for loop. (Array.entries() can be used to a similar effect.)

Examples

Invalid

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for (let i = 0; i < array.length; i++) {
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  console.log(array[i]);
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}

code-block.js:1:1 lint/style/useForOf ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ This for loop only uses its index to read from the iterated array.
  
  > 1 │ for (let i = 0; i < array.length; i++) {
      │ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  > 2 │   console.log(array[i]);
  > 3 │ }
      │ ^
    4 │ 
  
  ℹ A for…of loop expresses that pattern more clearly because it iterates over the array values directly.
  
  ℹ Use a for…of loop instead.

Valid

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for (let item of array) {
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   console.log(item);
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 }

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for (let i = 0; i < array.length; i++) {
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   // `i` is used, so for loop is OK
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   console.log(i, array[i]);
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 }

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for (let i = 0, j = 0; i < array.length; i++) {
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   console.log(i, array[i]);
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 }

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let i = 0;
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for (; i < array.length; i++) {
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   console.log(array[i]);
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 }