isUndefined

Checks if the given value is undefined.

This function tests whether the provided value is strictly equal to undefined. It returns true if the value is undefined, and false otherwise.

This function can also serve as a type predicate in TypeScript, narrowing the type of the argument to undefined.

Signature

function isUndefined(x: unknown): x is undefined;

Parameters

• x (unknown): The value to test if it is undefined.

Returns

(x is undefined): true if the value is undefined, false otherwise.

Examples

const value1 = undefined;
const value2 = null;
const value3 = 42;

console.log(isUndefined(value1)); // true
console.log(isUndefined(value2)); // false
console.log(isUndefined(value3)); // false