How to Check if Object is Array in JavaScript

JavaScript objects are powerful data structures that allow you to easily store different data types in a compact manner. Sometimes you may need to check if JS object is array in JavaScript. There are several ways to do this in JavaScript. In this article, we will learn how to check if object is array.

How to Check if Object is Array in JavaScript

Let us say you have the following JS object.

test = {'a':1, 'b':2}

Here are some of the ways to check if JS object is array in JavaScript.

1. Using Constructor

Every JS variable has constructor property available by default. You can simply use the constructor property of JS object to check if it is an array or not, as shown below. If it is an array then the constructor’s value will be Array.

test.constructor === Array
OR
test.constructor.name === "Array"

If you face issues with above command, first you can check if the constructor property is available or not.

test.prop && test.prop.constructor === Array

2. Using InstanceOf

You can also use InstanceOf keyword to check if variable is array or not.

test instanceof Array

3. Using Object.prototype

This is most complicated but also works for checking any data type not just arrays. The above two methods work only for checking if a variable is Array or not. You can use this method to check if a variable is string, or some other data type, just by changing [object Array] below to data type of your choice.

if(Object.prototype.toString.call(test) === '[object Array]') {
    alert('Array!');
}

In this article, we have learnt a few simple ways to check if a JS object is array or not. You can also use these methods to check if any variable, not just JS object, is array.

How to Check if Object is Array in JavaScript