undefined

@nick/is/undefined

isUndefined

Signature

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

Checks if the value is undefined, and nothing else.

Parameters

Name	Info
it	The value to check.

Returns

true if the value is undefined, or false otherwise.

Category

Primitives

Examples

import { isUndefined } from "jsr:@nick/is/undefined";

isUndefined(null); // false
isUndefined(undefined); // true
isUndefined(0); // false
isUndefined(void 0); // true
isUndefined(""); // false

import { isUndefined } from "jsr:@nick/is/undefined";

let value: number | undefined;
if (isUndefined(value)) {
  value;
  // ^? let value: undefined
  value = 0;
  // ^? let value: number | undefined
} else {
  value += 1;
  // ^? let value: number
}