How to Check if String Contains Substring (Case Insensitive) in Javascript

In this tutorial, you will learn how to check if string contains substring (case insensitive) in javascript. A subset of a string is known as a substring. For example, “test” is a substring of “My test”. From a developer perspective, it can be a bit tricky to find if a string contains a substring (case insensitive).

There are numerous ways to check if a string contains a substring (case insensitive). But for the sake of simplicity, we will use includes() method, toLowerCase() method, and ternary operator (?).

The includes() method is used to perform a case-sensitive search to detect whether a string contains another string or not and returns a Boolean value. The toLowerCase() method converts all letters in a string to lowercase.

In the following example, we have one global variable that holds a string. Upon click of a button, we will check if it contains a substring (case insensitive) 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 have str variable that hold a substring as its value. We will check if myString contains str.
  • We are converting both the strings into lowercase by calling toLowerCase() method so that we can perform case-insensitive check.
  • Further, we are using the includes() method to verify whether myString contains str substring or not. If it returns true, that means myString does contain str substring.
  • 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 = "Hello WORLD";

btnCheck.addEventListener("click", () => {

  let str = "orld",
  let result = myString.toLowerCase().includes(str.toLowerCase()) ? "Yes" : "No";
  output.innerText = result;