no-unnecessary-boolean-literal-compare
Disallow unnecessary equality comparisons against boolean literals.
Extending "plugin:@typescript-eslint/strict-type-checked"
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.).
module.exports = {
"rules": {
"@typescript-eslint/no-unnecessary-boolean-literal-compare": "error"
}
};
Examples
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) {
}
Options
This rule accepts the following options
type Options = [
{
/** Whether to allow comparisons between nullable boolean variables and `false`. */
allowComparingNullableBooleansToFalse?: boolean;
/** Whether to allow comparisons between nullable boolean variables and `true`. */
allowComparingNullableBooleansToTrue?: boolean;
},
];
const defaultOptions: Options = [
{
allowComparingNullableBooleansToTrue: true,
allowComparingNullableBooleansToFalse: true,
},
];
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.