Promise

A promise is an object representing the eventual completion or failure of an asynchronous operation, and its resulting value. It allows you to handle asynchronous operations in a more readable and manageable way compared to traditional callback-based approaches.

In JavaScript, many operations are asynchronous, such as fetching data from a server or reading a file. Traditionally, these operations are handled using callbacks, which can lead to callback hell (nested callbacks that are hard to read and maintain). Promises were introduced to provide a more elegant solution to this problem.

A promise can be in one of three states:

1. Pending: Initial state, neither fulfilled nor rejected.
2. Fulfilled: The operation completed successfully, and the promise now has a value.
3. Rejected: The operation failed, and the promise has a reason for the failure.

Example:

// Creating a promise
const myPromise = new Promise((resolve, reject) => {
    // Simulating an asynchronous operation
    setTimeout(() => {
        const success = true;
        if (success) {
            resolve('Operation completed successfully');
        } else {
            reject('Operation failed');
        }
    }, 2000);
});

// Consuming the promise
myPromise
    .then((result) => {
        console.log(result); // Output: Operation completed successfully
    })
    .catch((error) => {
        console.error(error); // Output: Operation failed
    });

In this example, myPromise represents an asynchronous operation that completes after 2 seconds. The then method is used to handle the successful completion of the operation, while the catch method is used to handle any errors.