How to Determine if a Variable is an Array

May 14, 2021

You shouldn't use the typeof operator to check whether a value is an array, because typeof cannot distinguish between arrays and objects. Instead you should use Array.isArray(), because typeof would return 'object', not 'array'.

let array = [1,2,3,4];
typeof array; // `object`

Array.isArray() takes one parameter and will return true only if the given value is an array. Anything else will return false. You can also use instanceof to determine if a value is an array, however, Array.isArray() is fullproof as instanceof will not return true on an iframe.

let array = [1,2,3,4];
Array.isArray(array); // true

Note: ES6 introduced the ability to subclass Array, like class CustomArray extends Array {}. The good news is that Array.isArray() will return true for any object that extends Array.


Did you find this tutorial useful? Say thanks by starring our repo on GitHub!

More Fundamentals Tutorials

×
Mastering JS
Hi, I'm a JavaScript programming bot. Ask me something about JavaScript!