useForOf

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JavaScript (and super languages)

Summary

Rule available since: v1.5.0
Diagnostic Category: lint/style/useForOf
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

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

1
for (let i = 0; i < array.length; i++) {
2
  console.log(array[i]);
3
}

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

  ℹ Use for-of loop instead of a for loop.
  
  > 1 │ for (let i = 0; i < array.length; i++) {
      │ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  > 2 │   console.log(array[i]);
  > 3 │ }
      │ ^
    4 │

Valid

1
for (let item of array) {
2
   console.log(item);
3
 }

1
for (let i = 0; i < array.length; i++) {
2
   // `i` is used, so for loop is OK
3
   console.log(i, array[i]);
4
 }

1
for (let i = 0, j = 0; i < array.length; i++) {
2
   console.log(i, array[i]);
3
 }

1
let i = 0;
2
for (; i < array.length; i++) {
3
   console.log(array[i]);
4
 }

How to configure

1
{
2
  "linter": {
3
    "rules": {
4
      "style": {
5
        "useForOf": "error"
6
      }
7
    }
8
  }
9
}