isUndefined

Checks if a given value is undefined.

const result = isUndefined(value);

Reference

isUndefined(value)

Use isUndefined when you want to check if a value is undefined. It's useful for checking whether a variable is initialized or whether an optional property exists.

import { isUndefined } from 'es-toolkit/predicate';

// undefined values
console.log(isUndefined(undefined)); // true
console.log(isUndefined(void 0)); // true

let uninitialized: string;
console.log(isUndefined(uninitialized)); // true

// Non-undefined values
console.log(isUndefined(null)); // false
console.log(isUndefined('')); // false
console.log(isUndefined(0)); // false
console.log(isUndefined(false)); // false
console.log(isUndefined({})); // false
console.log(isUndefined([])); // false

Parameters

• value (unknown): The value to check if it's undefined.

Returns

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