What are Promises in JavaScript?

JavascriptWeb DevelopmentObject Oriented Programming

Promises allow us to do asynchronous operations where the value is not known in advanced when the promise was being created. A promise can have three states pending, fulfilled and rejected.

Following is the code for promises in JavaScript −


 Live Demo

<!DOCTYPE html>
<html lang="en">
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
   body {
      font-family: "Segoe UI", Tahoma, Geneva, Verdana, sans-serif;
   .sample {
      font-size: 18px;
      font-weight: 500;
      color: red;
<h1>JavaScript Promises<h1>
<div class="sample"></div>
<button class="Btn">CLICK HERE</button>
<h3>Click on the above button to display username using promises</h3>
   let sampleEle = document.querySelector(".sample");
   document.querySelector(".Btn").addEventListener("click", () => {
      .then((response) => response.json())
      .then((result) => {
         result.forEach((element) => {
            sampleEle.innerHTML += element.username + "<br>";
      .catch((err) => alert(err));


The above code will produce the following output −

On clicking the ‘CLICK HERE’ button −

Updated on 17-Jul-2020 06:50:39