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Web applications, or web apps, are a huge part of the way the internet works! Facebook, Gmail (or any popular email website), and even Udacity’s classroom are examples of popular web apps. Let’s look at the big picture to see how web apps serve you dynamic web page content as you browse the internet.

First, let’s look at the difference between dynamic and non-dynamic websites. When visiting non-dynamic websites, your web browser will make the initial HTTP requests to download the HTML, CSS, and other files needed to create the initial webpage that you want to browse. But, once the web page is loaded, the web browser or the website won’t send any more HTTP requests to the web server to ask updates. What you see is what you get, until you click the refresh button.

On the other hand, dynamic web apps know how to build, or update, themselves on demand. More specifically, dynamic web apps often use JavaScript, Ajax, and/or long polling to make HTTP requests to the web server to ask for updates and new content (either on demand or on a regular cadence, depending on how the web app is built). If new updates are available, the web app will update itself accordingly.

Let’s look at the Facebook news feed as an example. Picture yourself in front of your computer, looking at your news feed in your favorite web browser.

This is what is happening under the hood: When you first load Facebook, which is a web app in this case, your browser will make the initial HTTP requests to build up your newsfeed for you. Once your news feed is pieced together, the Facebook web app will continue to talk to the Facebook servers via HTTP requests to ask for new updates, and if updates are available, your news feed will be updated accordingly. That’s why you’ll see new stories getting automatically added to your newsfeed, without pressing the refresh button.

In the early days of the internet, most of the content available online was static, but these days, most of the content on the internet is dynamic like Facebook.

Pretty cool to know what’s happening under the hood when you’re browsing the web, right? You can learn more in Udacity’s Full Stack Foundations free course, where you’ll learn to build a dynamic web app that displays restaurant menus.

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Want to learn even more? Check out the Intro to Programming Nanodegree program.