What is a Promise? What states does a Promise have?

Promise is an object in JavaScript/Node.js that represents the result of an asynchronous operation, which may succeed or fail in the future.

A Promise has three main states:

• pending: initial state, the operation is not yet completed.
• fulfilled: the operation completed successfully, and the Promise contains the result.
• rejected: the operation failed with an error.

Promises allow writing asynchronous code more readably, using .then() methods to handle success and .catch() for errors. The async/await syntax is also supported for more convenient asynchronous management.

Example:

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

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