How reliable is Internet Explorers browser mode?

Question

I can't seem to find any answers to this:

When i change the browser mode in IE, how much can I rely on it actually rendering the webpage as if it were lets say IE8 when I'm using IE10?

Answer 1

I'm seeing mixed results so far; I never tested the IE9 version, so cannot comment if Microsoft have done better job this time round (the kinds of things reported at https://stackoverflow.com/a/11418046/841830 are much more specific to CSS than I've been looking at).

Specifically I've installed IE10 on Windows 7 (64-bit), and tested HTML5 features. The selection of Document Mode appears to be much more important than the selection of Browser Mode.

• User agent changes correctly

• The IE detection idiom works

    &lt;!--[if lte IE 9]> &lt;script language="javascript"> var is_ie_9_or_earlier=true; &lt;</script> &lt;![endif]--> 

• typeof window.PostMessage : WRONG. this is being returned as "object" in IE7 mode. I believe it is undefined in real IE7. IE8/IE9/IE10 correctly return it as "object".

• typeof new XMLHttpRequest().responseType . This is "undefined" in IE7/IE8/IE9, and "string" in IE10. Which I believe is correct.
• typeof Object.keys . Undefined in IE7/IE8, but "function" in IE9/IE10. Again, I think this is correct.

On the other hand ietester on the same machine was much weirder (javascript not running correctly when it should have).