I don't believe there is a way to detect if the user's browser is in compat mode. Their user agent string will be determined by their browser mode, and their document mode will be determined by either the presence of an x-ua-compatible
meta tag (or header), or possibly by the doctype used.
Compatibility Mode was meant to protect the modern-browser-user from pages that relied on old and outdated features or hacks. It's not really something you would want to test against. Instead, write standards-compliant code which will be understood by the browser in either compat mode, or non-compat mode.
Here are the various results of differing Browser Modes and Document Modes:
Browser Mode: IE10 Compat View / Document Mode: IE7 standards
navigator.userAgent
"Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.2; WOW64; Trident/6.0;
.NET4.0E; .NET4.0C; Media Center PC 6.0; .NET CLR 3.5.30729;
.NET CLR 2.0.50727; .NET CLR 3.0.30729; BRI/2)"
document.documentMode
7
Browser Mode: IE7 / Document Mode: IE7 standards
navigator.userAgent
"Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.2; WOW64; .NET4.0E;
.NET4.0C; Media Center PC 6.0; .NET CLR 3.5.30729; .NET CLR 2.0.50727;
.NET CLR 3.0.30729; BRI/2)"
document.documentMode
7
As you can see, by these two methods there is no way to tell if the user is in compat view or not.
Overriding Compat View List
If your site appears on the compatibility view list, you can override their suggested rendering options by providng your own x-ua-compatible
header:
<meta http-equiv="x-ua-compatible" content="IE=9" />
This forces your browser into IE9 Standards Mode (no evaluation of the doctype). You could use IE=edge
to force it into the latest mode possible (on Internet Explorer 10, this would be IE 10 Standards), but this is not encouraged. Instead, set it to the latest mode you've tested with.
If the x-ua-compatible
header is set to IE10, but the user visits your page on an earlier browser, the nearest rendering engine will be used. For instance, if the user visits your page with IE9, and your meta tag instructs the browser to use IE10, the browser will fallback to IE9 Standards mode.
Note that IE=9
causes the browser to go into IE9 Standards Mode. It doesn't necessarily cause the browser to behave as though it were IE9. If you want the browser to behave as though it were IE9, you would want to use the EmulateIE9
content:
<meta http-equiv="x-ua-compatible" content="IE=EmulateIE9" />
This causes the browser to fallback on the DOCTYPE, if it's present, to determine whether the document mode will be Standards, or Quirks.
For further information, see Defining Document Compatibility.