#guard-for-in

#Configuration

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

export default defineConfig([
  js.configs.recommended,
  {
    rules: {
      'guard-for-in': 'error',
    },
  },
]);

#Rule Details

Require for-in loops to include an if statement. Iterating a for-in loop over an object exposes inherited prototype properties in addition to the object's own keys, so the body should typically be guarded (e.g. with Object.hasOwn, Object.prototype.hasOwnProperty.call, or a short-circuit continue) to filter unwanted properties.

Examples of incorrect code for this rule:

for (key in foo) {
  doSomething(key);
}

Examples of correct code for this rule:

for (key in foo) {
  if (Object.hasOwn(foo, key)) {
    doSomething(key);
  }
}

for (key in foo) {
  if (Object.prototype.hasOwnProperty.call(foo, key)) {
    doSomething(key);
  }
}

for (key in foo) {
  if (!Object.hasOwn(foo, key)) continue;
  doSomething(key);
}

#Original Documentation

• https://eslint.org/docs/latest/rules/guard-for-in