es-toolkit/docs/reference/predicate/isLength.md

isLength

Checks if a given value is a valid length.

This function tests whether the provided value is of type number, is a non-negative integer, and is less than or equal to JavaScript's maximum safe integer (Number.MAX_SAFE_INTEGER). It returns true if the value is a valid length, and false otherwise.

This function can also serve as a type predicate in TypeScript, narrowing the type of the argument to a valid length (number).

Signature

function isLength(value: unknown): value is number;

Parameters

• value (unknown): The value to check if it is a valid length.

Returns

(value is number): Returns true if the value is a valid length, otherwise false.

Examples

import { isLength } from 'es-toolkit/predicate';

const value1 = 0;
const value2 = 42;
const value3 = -1;
const value4 = 1.5;
const value5 = Number.MAX_SAFE_INTEGER;
const value6 = Number.MAX_SAFE_INTEGER + 1;

console.log(isLength(value1)); // true
console.log(isLength(value2)); // true
console.log(isLength(value3)); // false
console.log(isLength(value4)); // false
console.log(isLength(value5)); // true
console.log(isLength(value6)); // false