How to Convert Array Elements to Uppercase in Javascript

In this tutorial, you will learn how to convert array elements to uppercase in javascript. Array is a collection of elements and these elements can be of same data type or not. In case of string data type, we can have lowercase as well as uppercase strings. From a developer perspective, it can be a bit tricky to convert an array elements to uppercase.

There are numerous ways to convert an array elements to uppercase. But for the sake of simplicity, we will use map() method and toUpperCase() to accomplish our goal. The map() method calls a certain function for each element and return a new array. The toUpperCase() method converts a string into an uppercase string.

In the following example, we have one global array of strings. Upon click of a button, we will convert the array elements to uppercase and display the result on the screen.  Please have a  look over the code example and the steps given below.


  • We have 2 elements in the HTML file (button and ul).
  • The innerText for the button element is “Get”.
  • The ul element is empty for now and we will populate it dynamically using javascript.
  • 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">

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


  • We have a global variable users and it holds an array of strings.
  • We have the showUsers() method which is responsible for populating our ul element.
  • In showUsers() 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 the button element using the document.querySelector() method and attached a click event listener to it.
  • In the event handler function, we are using map() method and calling toUpperCase() method of each element to convert each element into lowercase.
  • Finally, we are calling showUsers() method to update the list of the users.
let users = ['Garry', 'Ryan', 'Dona', 'Mona'];

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


document.querySelector('button').addEventListener('click', () => {
    users = => item.toUpperCase());