#no-loop-func

#Configuration

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

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

Disallow function declarations that contain unsafe references inside loop statements.

#Rule Details

This is the TypeScript-aware version of the ESLint no-loop-func rule. It reports any function created inside a loop body that closes over a variable that may be modified across iterations, which typically indicates a mistake — every closure ends up reading the final value of the variable instead of the value at the time the closure was created.

Type-only references (used as TypeScript type annotations) are not flagged, because they have no runtime impact.

Examples of incorrect code for this rule:

for (var i = 0; i < 10; i++) {
  function foo() {
    console.log(i);
  }
}

for (var i = 0; i < 10; i++) {
  const handler = (event: Event) => {
    console.log(i);
  };
}

Examples of correct code for this rule:

for (let i = 0; i < 10; i++) {
  function foo() {
    console.log(i);
  }
}

let someArray: MyType[] = [];
for (let i = 0; i < 10; i += 1) {
  someArray = someArray.filter((item: MyType) => !!item);
}

type MyType = 1;
let someArray: MyType[] = [];
for (let i = 0; i < 10; i += 1) {
  someArray = someArray.filter((item: MyType) => !!item);
}

#When Not To Use It

If you do not want to be notified about functions defined inside loops, you can safely disable this rule.

#Original Documentation

• typescript-eslint/no-loop-func
• ESLint no-loop-func