If you decide to stop supporting all types of browsers, mainly older IE browsers, you’ll probably be required to detect the browser and it’s version using either client or server programming. Client browser detection can use viewed here. This blog entry focuses on an ASP.NET server side solution, which will allow not only to detect if the browser is supported, but on how to detect IE8 running in Compatibility View (optionally notifying the user on how to switch from this view to IE8).

The solution is quite simple - it relies on the user-agent string sent by the browser. Browsers send information to the server, one of them is HTTP_USER_AGENT, which describes the user’s browser. For example, IE browsers incorporate the keyword MSIE plus the browser’s version. So IE6 will show as MSIE 6, IE7 will show up as MSIE 7 and IE8 will show up as MSIE 8. But how will IE8 appear in Compatibility View (that is, IE7)? Apparently, the browser will send a string with MSIE 7. So, how can we tell whether this is really an IE7, or IE8 in Compatibility View? The answer relies also in the user-agent string: IE8 incorporates a new “Trident” token in the user-agent string, even in Compatibility View. So by combining a check for MSIE 7 with Trident, allows understanding that the user is running in Compatibility View.

In short, the following ASP.NET code will detect if the browser is running in Compatibility View:
bool isCompatibilityMode = (Request.UserAgent.IndexOf("MSIE 7") > -1 && Request.UserAgent.IndexOf("Trident") > -1);

Naturally, you may choose to refactor this code to “better looking code”, such as testing for IE first, and then testing for the major version of the browser etc’.

You can also combine this code in different scenarios: You can detect other browsers, you can block certain browsers, you can notify the users that they’re using unsupported browsers, and you can notify how to switch off Compatibility View etc’. It could also be a good practice to store the user’s decision in a Cookie, Session or some other Profile settings, in order not to process this code every time the browser makes a request.

You can read about the cause for this code in the first place in Browser Wars and Compatibility in Internet Explorer (Hebrew).

To see what your user agent is, click here.