prefer-for-of

Enforce the use of for-of loop over the standard for loop where possible.

🔒

Extending "plugin:@typescript-eslint/strict" in an ESLint configuration enables this rule.

Many developers default to writing for (let i = 0; i < ... loops to iterate over arrays. However, in many of those arrays, the loop iterator variable (e.g. i) is only used to access the respective element of the array. In those cases, a for-of loop is easier to read and write.

This rule recommends a for-of loop when the loop index is only used to read from an array that is being iterated.

.eslintrc.cjs

module.exports = {
  "rules": {
    "@typescript-eslint/prefer-for-of": "warn"
  }
};

Examples

❌ Incorrect

declare const array: string[];

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

✅ Correct

declare const array: string[];

for (const x of array) {
  console.log(x);
}

for (let i = 0; i < array.length; i++) {
  // i is used, so for-of could not be used.
  console.log(i, array[i]);
}

Options

This rule is not configurable.

When Not To Use It

If you transpile for browsers that do not support for-of loops, you may wish to use traditional for loops that produce more compact code.

Resources

• Rule source
• Test source