How to Check if a String is in a Set in Javascript

In this tutorial, you will learn how to check if a string is in a Set in javascript. The Set object in javascript allows you to store type agnostic values, which means you can store any value of any data type.

There are numerous ways to check if a string is in a Set. We are going to use one of the easiest solutions which involve the usage of the has() method and ternary (?) operator. The ternary operator is also known as the conditional operator which acts similar to the if-else statement. The has() method returns a boolean after checking whether a specified value exists in the Set object or not.

In the following example, we have one global variable and upon click of a button, we will check if a string is in a Set 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">

    <script src="script.js"></script>
body {
    text-align: center;

div {
    display: inline-block;

button {
    display: inline-block;
    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 a global variable myVar which holds a Set object as its value.
  • We have attached a click event listener to the button element.
  • In the event handler function, we are using has() method and ternary (?) operators to check if the string "john" is in the Set. 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 = new Set(['john', 'peter', 'marks']);

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

  let result = myVar.has('john')? "Yes" : "No";
  output.innerText = result;