Js Promises Async — Free Javascript Tutorial

TL;DR: Learn Js Promises Async in Javascript with a free, beginner-friendly tutorial, examples and practice for Indian students on Syllab.in.

Js Promises Async in Javascript

JavaScript is single-threaded. Asynchronous code (API calls, timers) uses callbacks or Promises to handle tasks that take time without blocking the page.

A Promise is an object representing a future value. States: pending → resolved (then) or rejected (catch). Use .then() to handle success, .catch() for errors.

async/await is syntactic sugar over Promises. An async function always returns a Promise. await pauses execution until the Promise resolves — making async code look synchronous.

Promise.all([p1, p2, p3]) runs all promises in parallel and resolves when all are done. Promise.race() resolves/rejects as soon as the first one does.

// Promise
const p = new Promise((resolve, reject) => {
  resolve(data);  // or reject(error)
});
p.then(data => console.log(data)).catch(err => console.error(err));

// Async/Await
async function fetchData() {
  try {
    const response = await fetch(url);
    const data = await response.json();
  

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