requireNonUndefined

function requireNonUndefined<T>(
  value: T | undefined,
  message: string = "Expected a defined value."
): T;

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
`value`	`T \\| undefined`	The value to validate.
`message` (optional) `= "Expected a defined value."`	`string`	The message of the exception. A default is used when omitted.

Returns

T — the same value, with undefined excluded from its type.

Throws

Exception	Condition
`IllegalArgumentException`	the value is `undefined`.

Examples

What passes and what does not

requireNonUndefined(null); // => null
requireNonUndefined(0); // => 0
requireNonUndefined(undefined); // throws IllegalArgumentException

Source

src/lang/base/requireNonUndefined.ts

23 September 2026

This documentation was generated with AI (Claude) from the library's source code.

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