How to Check if String Contains Only Uppercase in Javascript

In this tutorial, you will learn how to check if string contains only uppercase in javascript. Any content in the form of plain text is considered to be a string. A string generally contains a bunch of letters in the form of a text.  If those letters are written in uppercase, then that string is known as an uppercase string.

There are numerous ways to check if a string contains only uppercase. But for the sake of simplicity, we will use a strict equality operator (===) and toUpperCase() method to accomplish our goal. The toUpperCase() method converts a given string into a uppercase string.

In the following example, we have one global variable that holds a string. Upon click of a button, we will check if a string contains only uppercase and display the result 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 h1). The div element is just a wrapper for the rest of the elements.
  • The innerText for the button element is “Check” and for the h1 element, it 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">

  <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">


  <div class="container">    

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

.container {        
    text-align: center;

button {
  margin-top: 10px;
  padding: 10px 20px;


  • We have selected the button element and h1 element using the document.querySelector() method and stored them in btnCheck and output variables respectively.
  • We have attached a click event listener to the button element.
  • We have a global variable myString which holds a string as its value.
  • In the event handler function, we are using a strict equality operator (===) and the toUpperCase() method to check if myString is in uppercase. Depending upon the result of the check, we will assign “Yes” or “No” to the result variable.
  • We are displaying the result in the h1 element using the innerText property.
let btnCheck = document.querySelector("button");
let output = document.querySelector("h1");

let myString = "ABCDEF";

btnCheck.addEventListener("click", () => {
  let result = myString.toUpperCase() === myString ? "Yes" : "No";
  output.innerText = result;