no-unnecessary-boolean-literal-compare

Disallow unnecessary equality comparisons against boolean literals.

🔒

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

🔧

Some problems reported by this rule are automatically fixable by the --fix ESLint command line option.

💭

This rule requires type information to run.

Comparing boolean values to boolean literals is unnecessary: those comparisons result in the same booleans. Using the boolean values directly, or via a unary negation (!value), is more concise and clearer.

This rule ensures that you do not include unnecessary comparisons with boolean literals. A comparison is considered unnecessary if it checks a boolean literal against any variable with just the boolean type. A comparison is not considered unnecessary if the type is a union of booleans (string | boolean, SomeObject | boolean, etc.).

.eslintrc.cjs
module.exports = {
  "rules": {
    "@typescript-eslint/no-unnecessary-boolean-literal-compare": "error"
  }
};

Try this rule in the playground ↗

Examples

note

Throughout this page, only strict equality (=== and !==) are used in the examples. However, the implementation of the rule does not distinguish between strict and loose equality. Any example below that uses === would be treated the same way if == was used, and !== would be treated the same way if != was used.

❌ Incorrect
✅ Correct

declare const someCondition: boolean;
if (someCondition === true) {
}

declare const someCondition: boolean;
if (someCondition) {
}

declare const someObjectBoolean: boolean | Record<string, unknown>;
if (someObjectBoolean === true) {
}

declare const someStringBoolean: boolean | string;
if (someStringBoolean === true) {
}

This rule accepts an options object with the following properties:

interface Options {
  /**
   * Whether to allow comparisons between nullable boolean variables and `true`.
   */
  allowComparingNullableBooleansToTrue?: boolean;
  /**
   * Whether to allow comparisons between nullable boolean variables and `false`.
   */
  allowComparingNullableBooleansToFalse?: boolean;
}

const defaultOptions: Options = [
  {
    allowComparingNullableBooleansToTrue: true,
    allowComparingNullableBooleansToFalse: true,
  },
];

Options

This rule always checks comparisons between a boolean variable and a boolean literal. Comparisons between nullable boolean variables and boolean literals are not checked by default.

`allowComparingNullableBooleansToTrue`

Examples of code for this rule with { allowComparingNullableBooleansToTrue: false }:

❌ Incorrect
✅ Correct

declare const someUndefinedCondition: boolean | undefined;
if (someUndefinedCondition === true) {
}

declare const someNullCondition: boolean | null;
if (someNullCondition !== true) {
}

declare const someUndefinedCondition: boolean | undefined;
if (someUndefinedCondition) {
}

declare const someNullCondition: boolean | null;
if (!someNullCondition) {
}

`allowComparingNullableBooleansToFalse`

Examples of code for this rule with { allowComparingNullableBooleansToFalse: false }:

❌ Incorrect
✅ Correct

declare const someUndefinedCondition: boolean | undefined;
if (someUndefinedCondition === false) {
}

declare const someNullCondition: boolean | null;
if (someNullCondition !== false) {
}

declare const someUndefinedCondition: boolean | undefined;
if (someUndefinedCondition ?? true) {
}

declare const someNullCondition: boolean | null;
if (!(someNullCondition ?? true)) {
}

Fixer

Comparison	Fixer Output	Notes
`booleanVar === true`	`booleanVar`
`booleanVar !== true`	`!booleanVar`
`booleanVar === false`	`!booleanVar`
`booleanVar !== false`	`booleanVar`
`nullableBooleanVar === true`	`nullableBooleanVar`	Only checked/fixed if the `allowComparingNullableBooleansToTrue` option is `false`
`nullableBooleanVar !== true`	`!nullableBooleanVar`	Only checked/fixed if the `allowComparingNullableBooleansToTrue` option is `false`
`nullableBooleanVar === false`	`nullableBooleanVar ?? true`	Only checked/fixed if the `allowComparingNullableBooleansToFalse` option is `false`
`nullableBooleanVar !== false`	`!(nullableBooleanVar ?? true)`	Only checked/fixed if the `allowComparingNullableBooleansToFalse` option is `false`

Not To Use It

Do not use this rule when strictNullChecks is disabled. ESLint is not able to distinguish between false and undefined or null values. This can cause unintended code changes when using autofix.

Examples​

Options​

allowComparingNullableBooleansToTrue​

allowComparingNullableBooleansToFalse​

Fixer​

Not To Use It​

Resources​