nonUndefined
function nonUndefined<T>(value: T | undefined): value is T;
nonUndefined(value) is the same test as !isUndefined(value), written so that a guard clause reads as a sentence rather than as a negation.
The test is typeof value === "undefined", which is safe for a variable that was never declared, unlike a bare comparison.
isX and nonX answer a question and never interrupt control flow; requireX and requireNonX hand the value back or throw. The scheme is explained in Validation conventions.
Parameters
Parameter | Type | Description |
|---|---|---|
|
| The value to check. |
Returns
boolean — true when the value is not undefined; otherwise false.
In TypeScript the guard narrows value to T inside the branch.
Examples
What passes and what does not
nonUndefined(null); // => true
nonUndefined(0); // => true
nonUndefined(""); // => true
nonUndefined(undefined); // => false
See also
Source
23 September 2026
This documentation was generated with AI (Claude) from the library's source code.