How to Perform Case-insensitive Sorting of Array in JavaScript

In this tutorial, you will learn how to perform case-insensitive sorting of array in javascript. Case-sensitive sorting can be easily achieved using sort() and reverse() methods in javascript, but for case-insensitive sorting, you need to do a little extra work.

There are numerous ways to perform case-insensitive sorting and here, I am going to share one of my approaches in solving such a problem. As you know sort() method can take a compare function as a parameter and that function should return positive, negative, or 0 integer to decide sort order.

To accomplish our goal, we need to work on a custom compare function that takes 2 items from the array for comparison at a time.  Inside this compare function, we are going to use localeCompare() and toLowerCase() methods.

The localeCompare() method is responsible for comparison and it returns positive, negative, or 0 integer.  The toLowerCase() method makes sure that the string should be in lowercase before doing the comparison. I would suggest you to read MDN docs to learn about the localeCompare() method. 

In the following example, we will sort an array in ascending or descending order on a button click and display its items on the screen. Please have a look over the code example and the steps given below.


  • We have 3 elements in the HTML file (div, button, and ul). The div element is just a wrapper for the rest of the elements.
  • The first button element has “Ascending” and the second button element has “Descending” as innerText.
  • The ul element is empty for now since we will populate it dynamically using javascript.
  • 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">
  <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">
    <button id="btnAsc">Ascending</button>
    <button id="btnDesc">Descending</button>
  <script src="script.js"></script>
div {
    width: 15%;
    margin: auto;

button {
    padding: 10px;

li {
    font-size: 20px;
    font-weight: bold;
    margin-left: -30px;
    list-style: none;


  • We have a global variable users and it holds an array of strings.
  • We have the addUsers() method which is responsible for populating the ul element.
  • In the addUsers() method, we are simply looping through the users array and creating a template string with a bunch of li elements.
  • We are displaying that list in the ul element.
  • We have selected both the button elements by their ids using the document.querySelector() method and stored them in btnAsc and btnDesc variables respectively.
  • We have attached the click event listener to both the button elements.
  • In the event handler function of the ascending button, we are calling the sort() method and passing a custom compare function to it. Inside compare function, we are changing the case of both the items to lower using toLowerCase() method and doing comparison using localeCompare() method. Later, we are updating the list of users by calling the addUsers() method.
  • In the event handler function of the descending button, we are doing everything the same as we were doing for the ascending order, but we are also calling the reverse() method to change the order to descending.
let users = ['Peter', 'Marks', 'cathy', 'James', 'Sam'];

function addUsers(){
    let template = => `<li>${user}</li>`).join('\n');
    document.querySelector('ul').innerHTML = template;


let btnAsc = document.querySelector('#btnAsc');
let btnDesc = document.querySelector('#btnDesc');

btnAsc.addEventListener('click', () => {
    users.sort((a,b) => a.toLowerCase().localeCompare(b.toLowerCase()));

btnDesc.addEventListener('click', () => {
    users.sort((a,b) => a.toLowerCase().localeCompare(b.toLowerCase()));