Skip to content
Related Articles

Related Articles

How to check if a variable is an array in JavaScript?

Improve Article
Save Article
  • Last Updated : 10 Nov, 2022
Improve Article
Save Article

In JavaScript, we can check if a variable is an array by using 3 methods, using the isArray method, using the instanceof operator and using checking the constructor type if it matches an Array object.

Method 1: Using the isArray method 

The Array.isArray() method checks whether the passed variable is an Array object. 

Syntax:

Array.isArray(variableName)

It returns a true boolean value if the variable is an array and false if it is not. This is shown in the example below. 

Example-1: 

html




<!DOCTYPE html>
<html lang="en">
 
<head>
    <title>
        How to check if a variable
        is an array in JavaScript?
    </title>
</head>
 
<body>
    <h1 style="color: green">
        GeeksforGeeks
    </h1>
    <b>
        How to check if a variable
        is an array in JavaScript?
    </b>
    <p>
        Click on the button to check
        if the variable is an array
    </p>
    <p>Output for string:
    <div class="outputString">
    </div>
 
    <p>Output for number:
    <div class="outputNumber">
    </div>
 
    <p>Output for array:
    <div class="outputArray">
    </div>
 
 
    <button onclick="checkArray()">
        Click here
    </button>
    <script type="text/javascript">
        function checkArray() {
            let str = 'This is a string';
            let num = 25;
            let arr = [10, 20, 30, 40];
         
            ans = Array.isArray(str);
            document.querySelector(
            '.outputString').textContent = ans;
             
            ans = Array.isArray(num);
            document.querySelector(
            '.outputNumber').textContent = ans;
             
            ans = Array.isArray(arr);
            document.querySelector(
            '.outputArray').textContent = ans;
        }
    </script>
</body>
 
</html>


Output: 

isArray

Method 2: Using the instanceof operator 

The instanceof operator is used to test whether the prototype property of a constructor appears anywhere in the prototype chain of an object. This can be used to evaluate if an the given variable has a prototype of ‘Array’.

Syntax:

variable instanceof Array

The operator returns a true boolean value if the variable is same as what is specified (here an Array) and false if it is not. This is shown in the example below. 

Example-2: 

html




<!DOCTYPE html>
<html lang="en">
 
<head>
    <title>
        How to check if a variable is
        an array in JavaScript?
    </title>
</head>
 
<body>
    <h1 style="color: green">
        GeeksforGeeks
    </h1>
    <b>
        How to check if a variable is
        an array in JavaScript?
    </b>
    <p>
        Click on the button to check
        if the variable is an array
    </p>
    <p>Output for string:
    <div class="outputString"></div>
 
    <p>Output for number:
    <div class="outputNumber"></div>
 
    <p>Output for array:
    <div class="outputArray"></div>
 
 
    <button onclick="checkArray()">Click here</button>
    <script type="text/javascript">
        function checkArray() {
            let str = 'This is a string';
            let num = 25;
            let arr = [10, 20, 30, 40];
         
            ans = str instanceof Array;
            document.querySelector(
            '.outputString').textContent =
            ans;
            ans = num instanceof Array;
            document.querySelector(
            '.outputNumber').textContent =
            ans;
            ans = arr instanceof Array;
            document.querySelector(
            '.outputArray').textContent =
            ans;
        }
    </script>
</body>
 
</html>


Output: 

instanceof

Method 3: Checking the constructor property of the variable.

Another method to check a variable is an array is by checking it’s constructor with Array. 

Syntax:

variable.constructor === Array

This becomes true if the variable is same as what is specified (here an Array) and false if it is not. This is shown in the example below. 

Example-3: 

html




<!DOCTYPE html>
<html lang="en">
 
<head>
    <title>
        How to check if a variable is
        an array in JavaScript?
    </title>
</head>
 
<body>
    <h1 style="color: green">
        GeeksforGeeks
    </h1>
    <b>How to check if a variable is
        an array in JavaScript?</b>
 
    <p>Click on the button to check
        if the variable is an array</p>
 
    <p>Output for string:
    <div class="outputString"></div>
 
    <p>Output for number:
    <div class="outputNumber"></div>
 
    <p>Output for array:
    <div class="outputArray"></div>
 
 
    <button onclick="checkArray()">
        Click here
    </button>
    <script type="text/javascript">
        function checkArray() {
            let str = 'This is a string';
            let num = 25;
            let arr = [10, 20, 30, 40];
         
            ans = str.constructor === Array;
            document.querySelector(
            '.outputString').textContent = ans;
             
            ans = num.constructor === Array;
            document.querySelector(
            '.outputNumber').textContent = ans;
             
            ans = arr.constructor === Array;
            document.querySelector(
            '.outputArray').textContent = ans;
             
        }
    </script>
</body>
 
</html>


Output: 

constructor

JavaScript is best known for web page development but it is also used in a variety of non-browser environments. You can learn JavaScript from the ground up by following this JavaScript Tutorial and JavaScript Examples.


My Personal Notes arrow_drop_up
Related Articles

Start Your Coding Journey Now!