More than any other framework, React makes heavy use of JavaScript. If you want to be a kick-butt React developer, you need a solid grasp of JavaScript.

In particular, React takes advantage of a ton of modern JavaScript features, things like “destructuring assignment” and “rest/spread syntax”. If you're not familiar with this stuff, it makes React feel so much more confusing. Is this {...props} thing actually JavaScript, or is it some sort of React magic??

In this bonus module, we're going to explore the most pertinent features of the JavaScript language. We'll look at the most critical fundamentals, things like understanding the difference between statements and expressions. And we'll learn about modern JavaScript features, and how they're useful in a React context.

Unlike the modules in the course, this bonus module isn't really meant to be done in a linear fashion. It's more of a reference module.

As you go through the core course, you'll notice links to the lessons in this bonus module. When we build our own React in Module 1, for example, we need to know about DOM operations, and so there's a link to the “Interacting with the DOM” bonus lesson.

I recommend popping in and out of this module as-needed. There's nothing stopping you from going through it all at once, from start to finish, but it'd be a little bit boring. I think you'll have more fun using it as a reference, digging deeper into JavaScript principles as-needed, when you run into confusing situations or foreign syntax.