requireNaN

function requireNaN(value: unknown, message: string = "Expected NaN."): number;

Nothing is coerced first, which is where this differs from the global isNaN: that one converts its argument, so isNaN("abc") and isNaN(undefined) both report true.

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`	`unknown`	The value to validate.
`message` (optional) `= "Expected NaN."`	`string`	The message of the exception. A default is used when omitted.

Returns

number — the same value, typed as NaN.

Throws

Exception	Condition
`IllegalArgumentException`	the value is not the `NaN` number.

Examples

What passes and what does not

requireNaN(NaN); // => NaN
requireNaN(0 / 0); // => 0 / 0
requireNaN(0); // throws IllegalArgumentException
requireNaN("abc"); // throws IllegalArgumentException

Source

src/lang/number/requireNaN.ts

23 September 2026

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

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