Intro

JavaScript is known as a single-threaded programming language. We see this played out by JavaScript reading each line of code then implementing that line. What happens when I have my code retrieve some data that isn't explicitly in my code base (ex. an API call?). Well, if JavaScript did not have the ability to run processes asynchronously it would look like this:

Sync

As you can see, it took 60ms for our code to fully run through... Yes, we know we are talking in terms of milliseconds, but multiply that with a large number of users, this can quickly turn out to be seconds or, even worse, minutes.

Now let's see how using an async way of thinking can optimize the code base

Async

We see that the thread is not halting because of the external data retrieval. It continues to run, and once the async operation is finished, it then presents us with that information.

Keep in mind that one pitfall of optimization is complexity. Let's investigate further...

This is one of the major benefits of working with asynchronous code. But before we can get into building asynchronous code, let's explore the topic of Callbacks.