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