#no-for-in-array

#Configuration

import { defineConfig, ts } from '@rslint/core';

export default defineConfig([
  ts.configs.recommended,
  {
    rules: {
      '@typescript-eslint/no-for-in-array': 'error',
    },
  },
]);

#Rule Details

Disallows iterating over arrays with a for-in loop. Using for-in on arrays is problematic because it skips holes, returns indices as strings rather than numbers, and may visit inherited enumerable properties from the prototype chain. Use for-of, Array.prototype.forEach, or a standard for loop instead.

Examples of incorrect code for this rule:

const arr = [1, 2, 3];
for (const index in arr) {
  console.log(index); // "0", "1", "2" (strings, not numbers)
}

for (const key in ['a', 'b', 'c']) {
  console.log(key);
}

Examples of correct code for this rule:

const arr = [1, 2, 3];
for (const value of arr) {
  console.log(value);
}

arr.forEach((value, index) => {
  console.log(index, value);
});

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

#Original Documentation

• typescript-eslint no-for-in-array