To trigger IE into a compatibility mode, you can either send the X-UA-Compatible HTTP Header or use a META tag in your page's HEAD. If you don't do this, IE will run in normal mode.
If you want to check browser compatibility, one way to do so is by writing a jQuery AJAX call that attempts to use a JavaScript function known to not work in older versions of IE within a try-catch block, and then POST the result to your application.
For example, the trim() function doesn't work in IE8
var str = " Hello World! ";
var a = (str.trim());
if(a == "Hello World!"){
//Ajax Post true
} else {
//Ajax Post false
}
This approach should work because if enterprise mode is activated, it will function correctly within IE8.