I recently published the results of my JavaScript SEO experiment where I checked which JavaScript frameworks are properly crawled and indexed by Google. The results were shocking; it turns out Google has a number of problems when crawling and indexing JavaScript-rich websites.

Google managed to index only a few out of multiple JavaScript frameworks tested. And as I proved, indexing content doesn’t always mean crawling JavaScript-generated links.

This got me thinking. If Google is having problems with JavaScript crawling and indexing, how are Google’s smaller competitors dealing with this problem? Is JavaScript going to lead you to full de-indexing in most search engines?

If you decide to deploy a client-rendered website (meaning a browser or Googlebot needs to process the JavaScript before seeing the HTML), you're not only risking problems with your Google rankings — you may completely kill your chances at ranking in all the other search engines out there.

Google + JavaScript SEO experiment

To see how search engines other than Google deal with JavaScript crawling and indexing, we used our experiment website, http:/jsseo.expert, to check how Googlebot crawls and indexes JavaScript (and JavaScript frameworks’) generated content.

The experiment was quite simple: http://jsseo.expert has subpages with content parsed by different JavaScript frameworks. If you disable JavaScript, the content isn’t visible — i.e. if you go to http://jsseo.expert/angular2/, all the content within the red box is generated by Angular 2. If the content isn’t indexed in Yahoo, for example, we know that Yahoo’s indexer didn’t process the JavaScript.

Here are the results:

As you can see, Google and Ask are the only search engines to properly index JavaScript-generated content. Bing, Yahoo, AOL, DuckDuckGo, and Yandex are completely JavaScript-blind and won’t see your content if it isn’t HTML.

The next step: Can other search engines index JavaScript?

Most SEOs only cover JavaScript crawling and indexing issues when talking about Google. As you can see, the problem is much more complex. When you launch a client-rendered JavaScript-rich website (JavaScript is processed by the browser/crawler to “build” HTML), you can be 100% sure that it’s only going to be indexed and ranked in Google and Ask. Unfortunately, Google and Ask cover only ~64% of the whole search engine market, according to statista.com.

This means that your new, shiny, JavaScript-rich website can cost you ~36% of your website’s visibility on all search engines.

Let’s start with Yahoo, Bing, and AOL, which are responsible for 35% of search queries in the US.

Yahoo, Bing, and AOL

Even though Yahoo and AOL were here long before Google, they’ve obviously fallen behind its powerful algorithm and don’t invest in crawling and indexing as much as Google. One reason is likely the relatively high cost of crawling and indexing the web compared to the popularity of the website.

Google can freely invest millions of dollars in growing their computing power without worrying as much about return on investment, whereas Bing, AOL, and Ask only have a small percentage of the search market.

However, Microsoft-owned Bing isn't out of the running. Their growth has been quite aggressive over last 8 years:

Unfortunately, we can’t say the same about one of the market pioneers: AOL. Do you remember the days before Google? This video will surely bring back some memories from a simpler time.

If you want to learn more about search engine history, I highly recommend watching Marcus Tandler’s spectacular TEDx talk.

Ask.com

What about Ask.com? How is it possible that Ask, with less than 1% of the market, can invest in crawling and indexing JavaScript? It makes me question if the Ask network is powered by Google’s algorithm and crawlers. It's even more interesting looking at Ask’s aversion towards Google. There were already some speculations about Ask’s relationship with Google after Google Penguin in 2012, but we can now confirm that Ask’s crawling is using Google’s technology.

DuckDuckGo and Yandex

Both DuckDuckGo and Yandex had no problem indexing all the URLs within http://jsseo.expert, but unfortunately, the only content that was indexed properly was the 100% HTML page (http://jsseo.expert/html/).

Baidu

Despite my best efforts, I didn’t manage to index http://jsseo.expert in Baidu.com. It turns out you need a mainland China phone number to do that. I don’t have any previous experience with Baidu, so any and all help with indexing our experimental website would be appreciated. As soon as I succeed, I will update this article with Baidu.com results.

Going beyond the search engines

What if you don’t really care about search engines other than Google? Even if your target market is heavily dominated by Google, JavaScript crawling and indexing is still in an early stage, as my JavaScript SEO experiment documented.

Additionally, even if crawled and indexed properly, there is proof that JavaScript reliance can affect your rankings. Will Critchlow saw a significant traffic improvement after shifting from JavaScript-driven pages to non-JavaScript reliant.

Is there a JavaScript SEO silver bullet?

There is no search engine that can understand and process JavaScript at the level our modern browsers can. Even so, JavaScript isn’t inherently bad for SEO. JavaScript is awesome, but just like SEO, it requires experience and close attention to best practices.

If you want to enjoy all the perks of JavaScript without worrying about problems like Hulu.com’s JavaScript SEO issues, look into isomorphic JavaScript. It allows you to enjoy dynamic and beautiful websites without worrying about SEO.

If you've already developed a client-rendered website and can’t go back to the drawing board, you can always use pre-rendering services or enable server-side rendering. They often aren’t ideal solutions, but can definitely help you solve the JavaScript crawling and indexing problem until you come up with a better solution.

Regardless of the search engine, yet again we come back to testing and experimenting as a core component of technical SEO.

The future of JavaScript SEO

I highly recommend you follow along with how http://jsseo.expert/ is indexed in Google and other search engines. Even if some of the other search engines are a little behind Google, they'll need to improve how they deal with JavaScript-rich websites to meet the exponentially growing demand for what JavaScript frameworks offer, both to developers and end users.

For now, stick to HTML & CSS on your front-end. :)