asserts

The asserts() function throws when a predicate fails and narrows the input type when it passes.

Interactive example

Syntax

function asserts<
	GenericInput extends unknown,
	GenericPredicate extends GenericInput
>(
	input: GenericInput,
	predicate: (input: GenericInput) => input is GenericPredicate
): asserts input is GenericPredicate

Parameters

• input: The value to validate.
• predicate: A type-guard predicate used to validate and narrow the input.

Return value

Nothing. It throws an AssertsError when the predicate fails.

See also

• isType - Builds type guards based on runtime checks
• instanceOf - Type guard using constructors