Tell me what a Promise is in JavaScript.

A Promise in JavaScript is an object that represents the result of an asynchronous operation and allows you to work with it when the operation completes (successfully or with an error). A Promise can be in one of three states: pending, fulfilled, or rejected.

Example of using a Promise:

const promise = new Promise((resolve, reject) => {
  setTimeout(() => {
    const success = true;
    if (success) {
      resolve('Data received');
    } else {
      reject('Error');
    }
  }, 1000);
});

promise
  .then(result => console.log(result))
  .catch(error => console.error(error));

Promises help avoid "callback hell" and simplify reading and handling asynchronous code.