I recently installed Ghostery and am amazed by the number of JavaScript libraries being loaded on the sites I visit. Almost every site I visit has at least one analytics library, a few advertising libraries, and some social network sharing libraries.

To be a bit more quantitative, I pulled the libraries used by 20 of top sites to see if anything stood out. The biggest surprise was how differently the various types of sites used these libraries. Every single publisher used DoubleClick and yet only a quarter of them used Google Analytics while 80% of the social networks I looked at used Google Analytics and only 40% used DoubleClick. The other interesting piece was how many more libraries an average publisher uses compared to a social network or ecommerce site. Five of the 13 publishers I looked at included at least 20 JavaScript libraries while the most libraries included by a social network was 4, which was Pinterest. The bulk of these additional libraries tend to be advertising specific so it’s not that surprising that publishers have more of them but the difference in volume was shocking. I’ve included the data at the bottom of this post in case someone wants to take a stab at it but something on my todo list is to automate the process of gathering this info rather than relying on Ghostery and copy and paste. Once I get get it done I’ll follow up with another post analyzing the larger set of data.

Even if these libraries get cached in the browser it’s still quite a lot of JavaScript that’s executed every time a site is loaded. It’s insane that Forbes is loading 39 libraries every time a page is seen. I suspect most people use AdBlock not because of ads but because of the degraded performance of a site having to load these libraries and the associated images. I’m aware that publishers are in trouble but I don’t think adding more and more libraries to eke out additional revenue is a sustainable model.

# of Libraries by Site

# of Sites by Library

Avg # of Libraries by Site Type

Raw Data

You can also grab the entire set of data here.