July 7, 2020

How to Check if All Values in an Array are Equal in Javascript

By Krishnaa JavaScript Questions 0 Comments

In this tutorial, you will learn how to check if all values in an array are equal in javascript. In an array, we can store as many items as we want. Those items can be of similar type or different types.

If you are dynamically adding items to an array, then there is a possibility that maybe you are adding the same item again and again. The question here is, how you can figure this out and avoid such a thing from happening.

There are different solutions for this problem, but we will go with the simplest solution. Array type has every() method which you can use to check if all items in an array are meeting a certain condition.

In the following example, we have one global array and we simply want to verify if all items are equal using every() method. Please have a look over the code example and steps given below.

HTML & CSS

We have 3 elements in the HTML file (div, button, and h1). The div element is just a wrapper for the rest of the elements.
The inner text for the button element is “Check” and for the h1 element is “Result”.
We have done some basic styling using CSS and added the link to our style.css stylesheet inside the head element.

We have also included our javascript file script.js with a script tag at the bottom.

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <link rel="stylesheet" href="style.css">
    <title>Document</title>
</head>
<body>
    
    <div>
        <button>Check</button>
        <h1>Result</h1>
    </div>

    <script src="script.js"></script>
</body>
</html>

body {
    text-align: center;
}

div {
    display: inline-block;
}

button {
    display: inline-block;
    padding: 10px 20px;
}

Javascript

We have selected two elements button and h1 using the document.querySelector() method and stored them in btnCheck and result variables respectively.

We have a global variable users. users holds an array of strings.
We have attached the click event listener to the button element.
every() method takes an anonymous function as a parameter and returns a Boolean value. As you know, arrays have a 0-based index. This anonymous function will run for each item and simply check if each item is equivalent to the first item in the array.

We are setting the inner text of the h1 element to the Boolean value returned by the every() method.

let btnCheck = document.querySelector('button');
let result = document.querySelector('h1');

let users = ['Peter', 'Peter'];

btnCheck.addEventListener('click', () => {
    let isEqual = users.every(user => user == users[0]);

    result.innerText = isEqual ? 'True' : 'False';
});

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