detect IE and version number through injected conditional comments.js

//detect Internet Explorer and version number through injected conditional comments (no UA detect, no need for cond. compilation / jscript check)

//version arg is for IE version (optional)
//comparison arg supports 'lte', 'gte', etc (optional)

var isIE = (function(undefined){
  
  var doc = document,
    doc_elem = doc.documentElement,
    cache = {},
    elem;
  
  return function( version, comparison ) {
    if(/*@cc_on!@*/true){return false;}

    var key = [ comparison || '', 'IE', version || '' ].join(' ');
    
    if ( cache[ key ] === undefined ) {
      elem = elem || doc.createElement( 'B' );
      elem.innerHTML = '<!--[if '+ key +']><b></b><![endif]-->';
      cache[ key ] = !!elem.getElementsByTagName( 'b' ).length;
    }
    
    return cache[ key ];
  };
  
})();

//minified:
var isIE=(function(){var doc=document,doc_elem=doc.documentElement,cache={},elem;return function(version,comparison){if(/*@cc_on!@*/true){return false;}var key=[comparison||"","IE",version||""].join(" ");if(cache[key]===undefined){elem=elem||doc.createElement("B");elem.innerHTML="<!--[if "+key+"]><b></b><![endif]-->";cache[key]=!!elem.getElementsByTagName("b").length;}return cache[key];};})();
		
//is it IE?		
isIE(); 

//is it IE6?
isIE(6);

//is it less than or equal to IE 7?
isIE(7,'lte');

A cleaner way than that unused function argument, IMHO:

-- var isIE = (function(){
++ var isIE = (function(){var undefined;

Declaring a new variable named undefined overrides whatever it might be defined in the enclosing scope; and obviously, leaving it undefined makes it, well, function as undefined is intended to. (Personally, because I like allowing people to do evil hacks with undefined if they want, I use var u; in a new scope, instead, in most of my code.)

An IE-check ?

Have you considered ?:
var IE='\v'=='v';

http://ajaxian.com/archives/ievv
http://webreflection.blogspot.com/2009/01/32-bytes-to-know-if-your-browser-is-ie.html