Emulation Accuracy in Internet Explorer

Early preview versions of Internet Explorer 11 lacked Emulation features that we saw in Internet Explorer 9 and 10. When Windows 8.1 shipped, Internet Explorer 11 was found to have the Emulation features shipped with it. These tools are helpful, though they can be misleading at times.

My general workflow in the past when using these tools goes like this: A user reports an issue in Internet Explorer x. I instruct the latest version of Internet Explorer to emulate the reported version. If I encounter the same issue, I can debug using the modern version of Internet Explorer. If emulation does not reveal the same issue, I need to load up a virtual machine, or use a service like BrowserStack.

The problem with these tools is that it’s not entirely clear where the line of reliability resides. To what degree this emulation replicates the native experience is unknown (to me, at least). Due to this, I’ve decided to do a deep dive into Emulation and see just how reliable it is, and in which areas.

Computed Styles

The first dive wasinto Computed Styles. Does Internet Explorer generate the same computed styles as IE10 and IE9 when it is emulating those versions? Surprisingly, yes. Granted, I’m running instances of IE10 and IE9 in a Virtual Machine (compliments of modern.ie), so that should be considered. Also other important thing to note is that this pass-through assumes Standards Mode.

The comparison tables are being maintained in a Google Docs spreadsheet. Click the preview below for the full view.


Window Object

My next focus was on cycling over enumerable properties on the window object and laying those out for comparison. A cursory glance of this next table will reveal that Internet Explorer 11 emulates the window object from IE9 and IE10 very well. Granted, there are some very clear examples of where it brought along a couple extra methods and properties.


It’s worth noting that this particular table had to be done a couple of times. Some of these members don’t attach themselves to the window object until certain actions are performed. For instance, this table is front-loaded with a bunch of BROWSERTOOLS members that are pushed onto the window object when various portions of the developer tools are opened. Other members, such as $0, don’t exist until you perform an action like selecting an element in the DOM Explorer.