Detecting IE8 reliably using javascript

Question

I have written a web app that requires IE version 8 (or higher presumably). If I run IE8 on a clean windows install on a VM it reports 'MSIE 8.0' as a user agent when queried with navigator.userAgent in javascript. But on a colleagues windows 7 machine his IE reports version 8 in the Help|About window, but the user agent string is 'MSIE 7.0'.

I figure that somewhere on his machine there is a setting that's telling IE to spoof the previous version, some kind of compatibility setting I presume, but for the life of me I can't find it. I'm not setting up quirksmode or IE7 compatibility mode from my end.

Answer 1

The user agent is not a sensible or reliable way of determining the browser version. Why don't you look for the presence of the feature you require by making it IE8 only and use that? That is a much more reliable method.

Answer 2

http://www.modernizr.com/

It should detect such issues. Alternatively, I'm not sure but IE 8 might switch its User-Agent tag in 'Compatibility Mode'.

Answer 3

Could you use conditional comments?

<script>
  var is_ie8 = false;
</script>
<!--[if IE 8]>
  <script>
    is_ie8 = true;
  </script>
<![endif]-->

Answer 4

<meta http-equiv="X-UA-Compatible" content="IE=8">
<script type="text/javascript">
var is_ie8_or_better = false;
</script>
<!--[if gte IE 8]>
<script type="text/javascript">
is_ie8_or_better = true;
</script>
<![endif]-->

Answer 5

The only way I can figure out how to get my version of IE8 to say that it is IE7 is to enable Compatibility View. See http://blogs.msdn.com/b/ie/archive/2008/08/27/introducing-compatibility-view.aspx

Answer 6

Turns out his browser was set to display all 'intranet sites' in compatibility mode. Also, yes, compatibility mode changes the user agent string.