requireNonNaN

function requireNonNaN<T>(
  value: T | number,
  message: string = "Expected a value that is not NaN."
): T;

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`	`T \\| number`	The value to validate.
`message` (optional) `= "Expected a value that is not NaN."`	`string`	The message of the exception. A default is used when omitted.

Returns

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

Throws

Exception	Condition
`IllegalArgumentException`	the value is the `NaN` number.

Examples

What passes and what does not

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

Source

src/lang/number/requireNonNaN.ts

23 September 2026

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

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