Google’s Martin Splitt continues his JavaScript SEO video series with an episode explaining when JavaScript is worth worrying about.

He also identifies the uses of JavaScript that are not worth worrying about.

It’s not always necessary to be concerned about JavaScript with respect to SEO.

As Splitt explains, SEOs should only be concerned when they’re working with a “JavaScript site.”

What is a JavaScript site?

A site that uses JavaScript does not always qualify as a “JavaScript site.”

If all primary content can be viewed without loading JavaScript, then you have nothing to worry about.

On the other hand, if JavaScript is necessary for displaying critical content, then you’re working with a “JavaScript site.”

Another type of JS site is a single page app, which usually consists of a shell with various views displaying different content.

If you’ve ever used Instagram on a mobile browser then you’ve seen a good example of a single page app.

When Instagram is loaded in a mobile browser, the header and footer are static (the shell), while JavaScript is used to fetch and display the main content.

JavaScript frameworks such as Angular and React also fall into the category of single page apps.

When is JavaScript relevant for SEO?

JavaScript becomes relevant for SEO when it’s being used to dynamically load or modify critical content.

Ideally, Googlebot should be able to see all content on a page, including the parts that are being dynamically added using JavaScript.

So if you can view the page source and see all critical content, then JavaScript is not relevant to SEO in that instance.

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If you can only see some of the content in the page source, then that’s what will get indexed during the first wave of indexing.

The content that needs to be rendered using JavaScript will be indexed during the second wave.

Splitt explained two waves of indexing for JavaScript content in his previous video.

In later episodes, Splitt will go into more detail about improving JavaScript rendering during the second wave of indexing.