Promise

• A Promise in JavaScript is an object that represents a value that you don’t have yet, but will get in the future.

• It’s mainly used for asynchronous operations like fetching data from an API, reading a file, or waiting for a timer.

A Promise has three possible states:

• Pending – the work is still happening.

• Fulfilled – the work is done successfully.

• Rejected – the work failed.

Promises help you avoid callback hell and write cleaner asynchronous code.

Example:

const myPromise = new Promise((resolve, reject) => {
  let success = true;

  if (success) {
    resolve("Operation completed successfully!");
  } else {
    reject("Something went wrong.");
  }
});

myPromise
  .then(result => {
    console.log(result);  // Output: Operation completed successfully!
  })
  .catch(error => {
    console.log(error);   // Output: Something went wrong.
  });

What happens here?

• resolve() means the promise succeeded

• reject() means it failed

• then() runs when it succeeds

• catch() runs when it fails