Maintainable JavaScript

Chapter 12. Browser Detection

Browser detection is always a hot-button topic in web development. This battle predates JavaScript browser detection by a couple of years and begins with the introduction of Netscape Navigator, the first truly popular and widely used web browser. Netscape Navigator 2.0 was so far beyond any of the other available web browsers that websites began looking for its specific user-agent string before returning any useful content. This forced other browser vendors, notably Microsoft, to include things in their user-agent string to get around this form of browser detection.

User-Agent Detection

The earliest form of browser detection was user-agent detection, a process by which the server (and later the client) looked at the user-agent string and determined the browser. During that time, servers would regularly block certain browsers from viewing anything on the site based solely on the user-agent string. The browser that benefited the most was Netscape Navigator. Netscape was certainly the most capable browser, so websites targeted that browser as the only one that could properly display the site. Netscape’s user-agent string looked like this:

Mozilla/2.0 (Win95; I)

When Internet Explorer was first released, it was essentially forced to duplicate a large part of the Netscape user-agent string to ensure that servers would serve up the site to this new browser. Because most user-agent detection was done by searching for “Mozilla” and then taking the version ...