In JavaScript, the Promise.all() method is a powerful utility that allows you to combine multiple promises into a single promise. It takes an array of promises as an input and returns a new promise that resolves when all the input promises have resolved, or rejects if any of the promises reject.

Syntax

Promise.all(iterable);

The iterable parameter is an array (or any other iterable object) containing the promises to be resolved.

Usage

const promise1 = new Promise((resolve, reject) => {
  setTimeout(() => {
    resolve('Resolved Promise 1');
  }, 1000);
});

const promise2 = new Promise((resolve, reject) => {
  setTimeout(() => {
    resolve('Resolved Promise 2');
  }, 2000);
});

const promise3 = new Promise((resolve, reject) => {
  setTimeout(() => {
    resolve('Resolved Promise 3');
  }, 1500);
});

Promise.all([promise1, promise2, promise3])
  .then((results) => {
    console.log(results);
  })
  .catch((error) => {
    console.log(error);
  });

In the above example, we create three promises (promise1, promise2, promise3) that resolve after different intervals of time using the setTimeout() function. We pass these promises as an array to Promise.all().

When all the promises have resolved, the then() callback is invoked with an array of the resolved values. In this case, it will log ["Resolved Promise 1", "Resolved Promise 2", "Resolved Promise 3"] to the console.

If any of the promises reject, the catch() callback is invoked with the reason for rejection.

Handling Errors

If any of the promises in the input iterable reject, the Promise.all() method immediately rejects with the reason of the first rejected promise. The promises that are yet to resolve will be ignored.

To handle errors for individual promises, you can use the catch() method on each promise before passing them to Promise.all(). This way, you can handle errors separately for each promise.

Summary

The Promise.all() method in JavaScript provides a convenient way to handle multiple promises simultaneously. It allows you to wait for all promises to resolve and perform further actions when they have all completed successfully. By using Promise.all(), you can efficiently manage and synchronize asynchronous tasks in your JavaScript code.

Hashtags: #JavaScript #Promises