requireCountable

function requireCountable(
  value: unknown,
  message: string = "Expected a non-negative safe integer."
): number;

A value that can serve as a quantity, a length or a zero-based index: a whole number, not negative, and small enough that integer arithmetic on it is still exact.

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 a non-negative safe integer."`	`string`	The message of the exception. A default is used when omitted.

Returns

number — the same value, typed as a countable number.

Throws

Exception	Condition
`IllegalArgumentException`	the value is not a countable number.

Examples

What passes and what does not

requireCountable(0); // => 0
requireCountable(42); // => 42
requireCountable(-1); // throws IllegalArgumentException
requireCountable(1.5); // throws IllegalArgumentException

Source

src/lang/number/requireCountable.ts

23 September 2026

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

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