How Do You Check if a Character is Repeated in a String in Javascript

In this tutorial, you will learn how do you check if a character is repeated in a string in javascript. Since a string is formed by combining multiple characters, there is always a possibility that the string may or may not contain repeated characters.

There are numerous ways to check if a character is repeated in a string. We are going to use one of the easiest solutions which involve the usage of the RegExp object, match() method and ternary (?) operator.

The RegExp object is used for matching text in a string with a pattern. The match() methods matches a string against a regular expression. If the match is found, it returns an array of matches, otherwise returns null. The ternary operator is also known as the conditional operator which acts similar to the if-else statement.

In the following example, we have one global variable and upon click of a button, we will check if a character is repeated in the string 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 myVar which holds a string as its value.
  • In the event handler function, we are calling the isRepeated() method and passing myVar and character “a” as parameters. This method will check if the character “a” is repeated in the string and return a Boolean value.
  • In the isRepeated() method, we are using the RegExp constructor to create a RegExp object using the chr variable with a global flag (g). We are storing that object in the re variable.
  • We are calling match() method and passing re variable as a parameter. It will return an array of matches. If the number of items in the array is more than 1, that means the character "a" is repeated in the string.
  • 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 myVar = "Hi, how are you?";

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

function isRepeated(str, chr) {
  let re = new RegExp(chr, "g");
  let match = str.match(re);
  if (match) {
    return match.length == 1;
  return false;