How Google Crawls Javascript

I started blogging about the transition the Web is undergoing from a document to a programming model, from static to dynamic content, some time ago. This transition has very fundamental implications for Web archiving; what exactly does it mean to preserve something that is different every time you look at it? Not to mention the vastly increased cost of ingest, because executing a program takes a lot more, a potentially unlimited amount of, computation than simply parsing a document.

The transition has big implications for search engines too; they also have to execute rather than parse. Web developers have a strong incentive to make their pages search engine friendly, so although they have enthusiastically embraced Javascript they have often retained a parse-able path for search engine crawlers to follow. We have watched academic journals adopt Javascript, but so far very few have forced us to execute it to find their content.

Adam Audette and his collaborators at Merkle | RKG have an interesting post entitled We Tested How Googlebot Crawls Javascript And Here’s What We Learned. It is aimed at the SEO (Search Engine Optimzation) world but it contains a lot of useful information for Web archiving. The TL;DR is that Google (but not yet other search engines) is now executing the Javascript in ways that make providing an alternate, parse-able path largely irrelevant to a site's ranking. Over time, this will mean that the alternate paths will disappear, and force Web archives to execute the content.