JavaScript Promises

The Promise object represents the eventual completion (or failure) of an asynchronous operation and its resulting value.

Promise States

• Pending: Initial state of a promise, neither fulfilled nor rejected.

• Fulfilled: The operation completed successfully.

• Rejected: The operation failed.

Creating Promises

/* [Imp..] The new keyword is used to create a new instance of an 
object based on a constructor function */
const myPromise = new Promise((resolve, reject) => {
  // Asynchronous operation
  if (/* operation successful */) {
    resolve(result);
  } else {
    reject(error);
  }
});

Promise Methods:

1 . then(): Handles fulfillment of the promise.

myPromise.then(result => {
  // Handle fulfillment
})

2 . catch(): Handles promise rejection.

myPromise.catch(error => {
  // Handle rejection
});

3 . finally(): Executes after then() or catch(), regardless of the promise state.

myPromise.finally(() => {
  // Cleanup
});

3 . Promise.race(): Returns a promise that resolves or rejects as soon as one of the promises in the iterable resolves or rejects.

Promise.all([promise1, promise2, promise3])
  .then(results => {
    // All promises fulfilled
  }).catch(error => {
    // At least one promise rejected
  });

Chaining Promises

Promise chaining executes asynchronous operations sequentially with error handling.

promise1.then(result1 => {
  // Process result1
  return result2;
})
.catch(error => {
//Handle error for promise result 1 only
})
.then(result2 => {
  // Process result2
})
.catch(error => {
  // Handle any errors in the chain
});

Promises provide a powerful mechanism for handling asynchronous operations in JavaScript. Understanding these concepts will help you write cleaner and more efficient asynchronous code.