Update: As some of the comments mention, the technique below doesn't work anymore. It's best to use object detection to accomplish what you need, or use conditional comments. But if you need to detect IE6, this should work: /MSIE 6/i.test(navigator.userAgent)

Sometimes you just have to sniff for Internet Explorer 6 (and under) in JavaScript. Using conditional comments is a decent solution, but I don't want them scattered all over my code.

With a bit of help from Dean Edwards, I worked out the following:

var IE6 = false /*@cc_on || @_jscript_version < 5.7 @*/;

With just a single conditional comment, you can have a JavaScript variable that you can reuse throughout your code.

(IE6 will be true in Internet Explorer 6 and under, but does anyone really care about IE5 anymore? Thought not.)

You could use this technique to sniff for other things:

// exactly Internet Explorer 7
var IE7 = false /*@cc_on || @_jscript_version == 5.7 @*/;

// at least Internet Explorer 7
var gteIE7 = false /*@cc_on || @_jscript_version >= 5.7 @*/;


// any Internet Explorer (thanks to Dean)
var isMSIE = /*@cc_on!@*/false;

Note: browser sniffing is evil but sometimes painfully necessary.