#no-unsafe-negation

#Configuration

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

export default defineConfig([
  js.configs.recommended,
  {
    rules: {
      'no-unsafe-negation': 'error',
    },
  },
]);

#Rule Details

Disallows negating the left operand of relational operators. The code !a in b is parsed as (!a) in b, not !(a in b), which is usually not the intended behavior. The same applies to instanceof.

With the enforceForOrderingRelations option enabled, this rule also checks <, >, <=, and >= operators.

Examples of incorrect code for this rule:

if ((!key) in object) {
}

if ((!obj) instanceof Ctor) {
}

Examples of correct code for this rule:

if (!(key in object)) {
}

if (!(obj instanceof Ctor)) {
}

if ((!key) in object) {
}

#Options

#enforceForOrderingRelations

When set to true, also disallows negating the left operand of <, >, <=, and >= operators. Default is false.

Examples of incorrect code with { "enforceForOrderingRelations": true }:

if (!a < b) {
}

if (!a >= b) {
}

#Original Documentation

• ESLint no-unsafe-negation