When news came out the other day about Google’s move to host some of the more popular JavaScript libraries on their servers I was going to write a post about the privacy implications. As I sat down this morning to write that very post I came across another JavaScript related news story that trumped the one from Google.

SocialHistory.js is a brand new piece of JavaScript code that, while clever, is also a little bit disconcerting at the same time. This script allows a site to determine what social networking (or regular sites) a visitor has previously visited. The creator of the script uses the example of implementing this to determine what social bookmarking links to provide on a page.

My first thought was the amount of market research a person could collect with this. What’s stopping me from taking the script, slightly modifying it so that it actually stores the data is collects and then using that data to determine if making pushes to promote my site on certain social networks would be worth my time? The answer is probably nothing.

But is that a good idea? The data is probably relatively harmless. For instance, the script can tell that I personally use sites like Facebook and del.icio.us but that’s true for, quite literally, hundreds of thousands of people. Maybe the data you could gather from SocialHistory.js to use for research means wouldn’t prove to be very valuable in the long term but I’m just not sure it’s any of my business to see that information in the first place.