lengthEqual

The lengthEqual() function checks that an array contains exactly a given number of elements. It acts as a type guard to infer a fixed-length tuple.

Interactive example

Syntax

Classic signature

function lengthEqual<
	GenericArray extends readonly unknown[],
	GenericLength extends number
>(
	array: GenericArray,
	length: GenericLength
): array is CreateTuple<GenericArray[number], GenericLength>

Curried signature

function lengthEqual<
	GenericArray extends readonly unknown[],
	GenericLength extends number
>(
	length: GenericLength
): (
	array: GenericArray
) => array is CreateTuple<GenericArray[number], GenericLength>

Parameters

• array: Array for which you want to guarantee the exact length.
• length: Expected length.

Return value

true if the array length equals length, otherwise false. When the function returns true, the array type is narrowed to a fixed length.

See also

• minElements - Checks a minimum number of elements
• maxElements - Checks a maximum number of elements
• length - Returns the exact size of an array

Sources

• MDN Web Docs - Array.length