How to Wait for All Promises to Resolve in JavaScript

In JavaScript, there are situations where we need to wait for multiple promises to resolve before continuing the execution of our code. Instead of waiting for one promise to resolve and then starting the next one, it would be more efficient to start all the promises simultaneously and wait for all of them to finish. In this blog post, we will discuss how to achieve this using the await keyword and the Promise.all() method.

Let’s consider an example where we have two promises: store.getAll() and store.getAllKeys(). Our goal is to start both promises and wait until both of them are resolved.

The traditional approach would be to use separate await statements for each promise, like this:

const values = await store.getAll();
const keys = await store.getAllKeys();

Although this approach works, it is not ideal because we are waiting for the first promise to resolve before starting the second one. This can introduce unnecessary delays in our code execution.

To improve this, we can wrap both promises in a Promise.all() call, which allows us to wait for all promises to resolve in parallel. Here’s how we can implement it:

const data = await Promise.all([store.getAll(), store.getAllKeys()]);

By using Promise.all(), we start both promises simultaneously and wait until both of them are resolved. The result is an array data, where the first element (data[0]) represents the resolved value of the first promise (store.getAll()), and the second element (data[1]) represents the resolved value of the second promise (store.getAllKeys()).

Using this approach, we can ensure that our code waits for all promises to resolve before proceeding. This can significantly improve the efficiency and performance of our JavaScript applications.