Detect older IE versions

Question

I need to detect if the user is running an older version of IE (IE9 is fine) from a jQuery plugin, so I won't have control over the HTML.

We've been discouraged from parsing the user-agent string and using $.browser.msie. The $.support method doesn't cover the problem either.

So, I figured out that this works, but I'm not sure if it is "good practice".

$('body').append('<!--[if lte IE 8]><script>$("body").addClass("oldie");</script><![endif]-->');
var old_ie = $('body').is('.oldie');

Would you use this method or stick with parsing the user-agent string (I'll need to figure out if it's IE and get the version number)?

Answer 1

You can run this

var ie = (function () {
    var undef, v = 3, div = document.createElement('div');

    while (
        div.innerHTML = '<!--[if gt IE '+(++v)+']><i></i><![endif]-->',
        div.getElementsByTagName('i')[0]
    );

    return v > 4 ? v : undef;
}());

to detect the version of IE.

Source: http://ajaxian.com/archives/attack-of-the-ie-conditional-comment

And then

if ( ie < 9 ) {
    // do your stuff, for instance:
    window.location = 'http://getfirefox.com'; // :p
}

Answer 2

You didn't explicitly mention in your question why you had a specific need to detect for IE9, so in general the following advice holds:

Rather than detecting for a specific browser / version, you should instead be detecting for specific features. Modernizr is a good place to start for help with this.