Now that we've seen a hands-on example of how JavaScript can be used with Python, let's discuss its uses across the frontend spectrum. Spoiler alert: we'll be using JavaScript on the server side, starting in the next chapter. We encountered some cryptic commands in our Ajax example, so while it may be easy to overlook the use of and need for JavaScript, we see it's a real language with real applications.
Part of the beauty of JavaScript is its nearly universal adoption in browsers. Over time, JavaScript syntax and features have slowly evolved, but support for the different features, which were at one time wildly different between browsers, is now standardizing. Some differences still remain, however, but there are useful tools on the web that are kept up to date on the various features that browsers may or may not support. One of these sites is caniuse.com, and this is illustrated in the following screenshot:
The various methods and properties of JavaScript are broken out in this site by various popular browsers in a matrix to show which are (and which are not) supported by each browser. In general, however, you won't need to worry too much about whether or not your code will run on a given browser unless you're using cutting-edge features.
Now, we've shown an example of JavaScript interacting with Python as our backend using Flask, but we can use practically any backend system, as long as it's prepared to accept inbound HTTP traffic. Python, PHP, Ruby, Java—the possibilities are all there, as long as the backend expects to be working with a frontend.
A note about libraries such as jQuery: we won't be using jQuery in this book. While useful for shortcuts and simplification of some methods, one of its major draws (at least for many developers such as myself) was its under-the-hood standardization of JavaScript between browsers. Remember that Ajax fetch call we made? It used to be the case that an Ajax call had to be written in two different ways, one for each main type of JavaScript interpreter. However, browser standardization has eased most of the cross-browser nightmares. jQuery still provides many tools that are useful, especially for the user interface (UI), such as plugins that make it unnecessary to write components from scratch. Whether or not you use jQuery or similar libraries is up to you or will be dictated by the project's needs. Libraries such as React, which we will be discussing, are designed to fill a very different need than libraries such as jQuery.
