 There are many different kinds of content on the web. There is HTML, images and videos, but also increasingly complex applications running in the browser for things such as email, spreadsheets or even entire photo editing suites. So, what does the term JavaScript site really mean and when do you need to pay attention to JavaScript SEO? Traditionally, JavaScript was used to progressively enhance the site on top of its primary content. For example, you may add behavior or additional features such as analytics, funky text effects that follow the mouse cursor or even whimsical effects such as falling snowflakes on a web page. We don't refer to such websites as JavaScript sites because all their primary content is present without JavaScript. Try this for yourself and use the view page source feature of your browser. Alternatively, you can also turn off JavaScript in your browser and these sites will still work just fine and show you all their primary content. But then there are these websites that use JavaScript to load and display critical content such as using JavaScript to dynamically load more content when the user scrolls or when the browser is resized. JavaScript might also be used to do other things in response to user actions such as clicking or typing on a keyboard. The important difference from the previous examples of using JavaScript for dynamic behavior is that now we are using JavaScript to modify or add critical content on the page. This is relevant for SEO purposes as you want to make sure that Googlebot sees all the content on the page including the parts that are being dynamically added using JavaScript. Last but not least, they are the so-called single page apps. Single page apps usually consist of the so-called shell and various views or routes with different content. Some JavaScript frameworks like React and Angular fall into this category as well. For example, you might have a shell consisting of a navigation menu and a footer that stay the same all the time. But in between navigation and footer, the content can change without reloading the page. You can use the browser's developer tools to see the content being fetched from the network in these cases. Unlike the previous examples of websites using JavaScript, single page applications usually only deliver the static parts, the shell, and use JavaScript to decide which content to fetch and display later. So let's take a step back and recap. If you use the view page source of your browser and see all your content, you don't have to worry about JavaScript SEO. If you only see some of your content, this content will be indexed in the first wave of indexing, so right away basically. We will have a look at some tools and tips to make sure the rest of your content remains indexable as well. If you are concerned with being indexed as fast as possible, make sure the content you care about the most is part of the markup you see in the source of your website. If you do not see your content and use JavaScript to load the content dynamically, that means your single page app will need to wait for rendering and then indexing. In later episodes, we will explore options to improve this. For instance, we can use dynamic rendering, but don't worry. This won't affect how your website is ranking or place your site at a disadvantage. In the next episode, we will go over a few important techniques and best practices that you should keep in mind no matter what kind of site you have to make sure your site's content is discoverable in search. So do not forget to subscribe and comment and like this video and also check the helpful webmasters links in the video description below. More JavaScript SEO is coming soon, so stay tuned!