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Hi everyone, I'm Guil, a JavaScript teacher here at Treehouse.

JavaScript is the most popular and

versatile programming language in the world.

And there's a lot of ground to cover on the subject.

In this course, you'll take a short break from coding and

continue to explore the exciting JavaScript echo system.

You'll learn how Node.js help JavaScript reach new heights.

Discover applications and tools built with JavaScript.

And get a closer look at popular JavaScript frameworks, libraries and more.

JavaScript was originally designed to run in the browser.

But JavaScript can be found in other places too.

For instance, JavaScript is the only web-based

programming language that can run on both the front end and the back end.

So let's delve into what this means.

Writing JavaScript that runs on the front end or

client side means you're writing JavaScript that runs in the browser.

Client-side JavaScript is what allows user interactivity in web pages.

JavaScript is interpreted and executed by the browser's JavaScript engine against

browser specific APIs, like the DOM, or Document Object Model, for example.

The JavaScript you've written in many of the projects so far at Treehouse, for

example, is client-side JavaScript.

You linked a JavaScript file to an HTML file and tested and

viewed the results of your code in the browser.

You may have selected and

manipulated elements with JavaScript too, or used JavaScript for form validation.

So client-side JavaScript is mainly concerned with improving and

enhancing the appearance and behavior of the rendered web page.

Google Maps is a popular example of an application that uses client-side

JavaScript to let you interact with a map by moving it around, zooming in and

out, and more.

But JavaScript is not just about working with the DOM.

Writing back end or server-side JavaScript means that instead of writing code

that executes in the browser, you're writing code that executes on the server.

Server-side JavaScript is used for building APIs, databases,

web servers, and more.

Instead of dealing with the rendered page only, server-side JavaScript can be used

to provide customized experiences for each user's request to a website.

Writing JavaScript for both the front end and

back end portions of an application is known as Full-Stack Development.

How was JavaScript able to run in different environments?

Well, host objects are supplied to JavaScript by the environment.

That way, JavaScript code can execute in that specific environment.

For example, the browser provides the window object for working with the DOM.

The browser also provides document, history, XMLHttpRequest,

and other host objects.

Now Node, a Server-side runtime environment for

JavaScript, provides a completely different set of host objects,

which you'll learn about in the next video.

For now, you can read more about host objects in the teacher's notes.

JavaScript's Native Objects are available to you, no matter the environment.

Native Objects are the built-in objects that

are part of the JavaScript programming language.

Like the string, number, array, and math objects for example.

They're available in both the browser and server-side environments like Node.JS.

Speaking of Node, in the next video, we'll explore this powerful tool that can run

JavaScript applications on the server side, client side, and

just about anywhere else.