? JavaScript Promises

A Promise is an object that represents the eventual completion (or failure) of an asynchronous operation and its resulting value.

Why Use Promises?

Before Promises, handling async tasks like network requests or timers led to "callback hell"—deeply nested callbacks hard to manage.

Promises allow you to write cleaner, more manageable asynchronous code.

Promise States

• Pending: Initial state, operation not completed yet.

• Fulfilled: Operation completed successfully.

• Rejected: Operation failed.

Creating a Promise

const myPromise = new Promise((resolve, reject) => {  // async operation  let success = true; // simulate outcome  if (success) {    resolve("Operation succeeded!");  } else {    reject("Operation failed!");  }});

Using Promises: .then() and .catch()

myPromise  .then(result => {    console.log(result); // "Operation succeeded!"  })  .catch(error => {    console.error(error); // If rejected, logs error message  });

Example: Simple Promise with setTimeout

function wait(ms) {  return new Promise((resolve) => {    setTimeout(() => {      resolve(`Waited for ${ms} milliseconds`);    }, ms);  });}wait(2000).then(message => console.log(message));

Chaining Promises

You can chain multiple .then() calls to run sequential async operations:

wait(1000)  .then(msg => {    console.log(msg);    return wait(2000);  })  .then(msg => console.log(msg));

Promise.all()

Wait for multiple promises to resolve in parallel:

Promise.all([wait(1000), wait(2000), wait(1500)]).then(messages => {  console.log(messages);});

Summary

Want me to explain async/await which is syntactic sugar over Promises?