There is no DOM property that indicates that you're running EMIE. The whole idea of EMIE is to emulate IE8 behavior better than the IE8 document mode emulates IE8 behavior. EMIE should only be used in specific cases where it's needed; it should not be used wholesale.
It is possible to detect EMIE in certain cases. If you look carefully at the list of user-agent strings over the last couple of releases, there's a noticeable difference between EMIE on IE11 and the user agent string for IE11 RTM.
However, before you take that as your magic bullet, there are two caveats:
You cannot disable EMIE programmatically. It's a local configuration change only.
The user agent for IE11 is completely different today than it was when IE11 was released. Based on reports from the IE team, the UA string is going to be even more complicated, especially once "IE Spartan" (or whatever they choose to call it") hits the wire.
My recommendation? Create a small launcher page that does a simple feature detection for the web app in question. If you detect features consistent with what's needed for the app, then display a link to launch the app. If feature detection fails to detect IE8, IE11, or whatever version you've targeted, display a warning with a link to more troubleshooting information. Be sure to include a launch link anyway, just in case.
This way, the user has the information they need and you have a lightweight way of handling the issue, one that doesn't require too many updates to the app in question.
Hope this helps...
-- Lance
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…