How to Check if String is Lowercase in Javascript

In this tutorial, you will learn how to check if string is lowercase 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 lowercase, then that string is known as a lowercase string.

Most of the websites prefer username to be in lowercase and this is when it becomes very important to know how to verify if that username is in lowercase or not. This tutorial is definitely going to give you an idea about how you can accomplish that in a simple and easy way.

There are numerous ways to detect whether a string is in lowercase or not. But for the sake of simplicity, we will use a strict equality operator (===) and toLowerCase() method to accomplish our goal. The toLowerCase() method converts a given string into a lowercase string.

In the following example, we have one global variable that holds a string. Upon click of a button, we will check whether it is in lowercase or not 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 toLowerCase() method to verify whether myString is in lowercase or not. 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.toLowerCase() === myString ? "Yes" : "No";
  output.innerText = result;