Type/Since 1.38.0

isNil

Checks whether a value is null or undefined and provides a TypeScript type guard for nullish values.

isNil(value):value is null | undefined

Implementation

The function explicitly compares the value with null and undefined using strict equality.

The return type `value is null | undefined` makes the function a TypeScript type guard for nullish values.

Only null and undefined return true. Other falsy values such as false, 0, and an empty string return false.

valueunknownrequired

The value to check.

value is null | undefined

Returns true when the value is null or undefined; otherwise returns false.

Check for nullish values.

TypeScript

isNil(null);
// true

isNil(undefined);
// true

isNil("hello");
// false

The type guard narrows the checked value to null | undefined when the condition succeeds.

TypeScript

const value: string | null | undefined = null;

if (isNil(value)) {
  // value is narrowed to null | undefined
}

Other falsy values such as false, 0, and an empty string are not considered nil.

TypeScript

isNil(false);
// false

isNil(0);
// false

isNil("");
// false

Objects and arrays are not considered nil values.

TypeScript

isNil({});
// false

isNil([]);
// false

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