Promises

A Promise is an object that represents the eventual completion (or failure) of an asynchronous operation and its resulting value. It provides a robust way to handle asynchronous tasks like fetching data from a server, reading a file, or waiting for a timer, without blocking the main thread of execution. A Promise can be in one of three states: *pending* (the initial state, operation hasn't completed), *fulfilled* (the operation completed successfully), or *rejected* (the operation failed). Promises are a massive improvement over the older callback-based approach, which often led to deeply nested, unreadable code known as 'callback hell'. With Promises, you can chain asynchronous operations using the `.then()` method, which is called when the promise is fulfilled, and handle errors for the entire chain in a single `.catch()` block. This leads to a more linear and readable code structure. You can create your own Promises using the `new Promise()` constructor, which takes a function with `resolve` and `reject` arguments. You call `resolve` with the result on success and `reject` with an error on failure. Understanding Promises is essential for modern asynchronous JavaScript.