Understanding JavaScript Rendering: a Beginner Guide

If you work in the digital space – whether as a developer, an SEO, or in marketing in general – you are bound to come across JavaScript at some point. Although you might not want to, as it may seem daunting and overwhelming, you will probably have to teach yourself the basics at some point. And that’s where this beginner’s guide comes in to help.

We’re going to take you through the basics of JavaScript. In particular, we’ll explain in a bit more detail what JavaScript rendering is, how search engines render JavaScript, and what this means for you and your (company’s) website.

After reading this short introductory guide, you will have a better understanding of the fundamentals of JavaScript and the rendering process. Ready to dive in? Let’s go!

What is JavaScript?

Let’s start by defining what JavaScript actually is. JavaScript, or JS for short, is a programming language that is part of the very foundation of the World Wide Web.

It is one of the three core technologies of the web, together with Hypertext Markup Language (HTML) and Cascading Style Sheets (CSS). Each technology is responsible for a specific part of a web page’s build-up:

In other words, JavaScript is the technology that brings a page to life. Without it, pages would be static instead of interactive, still instead of animated.

JavaScript language has all sorts of applications across the web, from creating interactive web pages to something like using a Google search API like SERPMaster for scraping purposes. You can see why JavaScript is such an essential part of the Internet!

Now despite its great use, JavaScript does pose some problems. In particular, search engines aren’t that great (yet) at understanding – and thus indexing – pages containing many JavaScript elements. And that has to do with the rendering process.

What is rendering?

Rendering in the context of web development is the process of fetching data from a page and processing this data to produce the required output/result.

It is how programming languages are turned into understandable, structured code that, in turn, is turned into the site you see in front of you when you open a web page. This rendering process is an essential step in correctly displaying a web page to the user. See this step as interpreting the raw data.

Now basic HTML is easily rendered (that is, interpreted) by a browser or robot as it contains all the content that is on the page. When the page contains JavaScript, on the other hand, it is a bit more complicated.

That is because to understand the meaning of JavaScript code the browser first has to run the specific script referred to in the code to reveal the full content on the page.

This makes JavaScript rendering more difficult than the interpretation of plain HTML.

How search engines render JavaScript?

Now a particular problem with JavaScript rendering occurs when search engine robots (crawlers) need to render a web page with JavaScript.

Some search engines aren’t capable of rendering JavaScript at all, while others (including industry-giants Google and Bing) struggle to do so.

So if your website has a lot of JavaScript elements there is a chance that search engines (or well, their robots) aren’t able to understand what’s on your page and mistakenly think there is no content to see. Since the bot thinks there’s nothing to see, it won’t include your page in its index.

In other words, you won’t show up in the search engine results pages (SERPs). And without showing up in the SERPs, you have little chance of being found by customers. This way, you’ll be out of business before you know it, no matter how great your website looks with all those beautiful JavaScript elements!

So why is JavaScript rendering so difficult for search engines?

Let’s have a look at Google as an example. The search engine’s web crawler, Googlebot, processes JavaScript in three stages:

  1. Crawling
  2. Rendering
  3. Indexing

The bot first crawls a web page by sending a request to the server, which is returned with the HTML response. Before Googlebot is able to fully understand the HTML response containing JavaScript it has to render it. Once rendered, the interpreted HTML file is ready for indexing in the search engine.

The indexing process of Google works in two waves: crawling and indexing, and rendering and indexing.

Now crawling and indexing are relatively quick processes that can be done simultaneously, but rendering requires a bit more time and processing power. So if Googlebot crawls a page and finds JavaScript, it places the page in the rendering queue where it will remain until there are enough resources available to render the page.

However, the unrendered data will already have been added to the index during the first wave of indexing. And once your web page gets stuck between these two waves, newly added content won’t be indexed by the search engine.
Luckily, there are ways to properly write your pages – including JavaScript – to make them easier to process for Google. You can find all the latest best-practices in Google Search Central. This way, your SEO performance won’t suffer as a result of your beautiful website!

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