如何判断是否为IE浏览器,以及IE浏览器的版本号(IE6,IE7,IE8,IE9)

var isIE = function(ver){
    var b = document.createElement('b')
    if(ver){
    	b.innerHTML = '<!--[if IE ' + ver + ']>1<![endif]-->';
    	return b.innerHTML == 1;
    }else{
    	var ver = '';
    	b.innerHTML = '<!--[if IE ' + ver + ']>1<![endif]-->';
    	return b.innerHTML == 1;
    }
    
}
alert('ie6:' + isIE(6) + '\n' + 'ie7:' + isIE(7) + '\n' + 'ie8:' + isIE(8) + '\n' + 'ie9:' + isIE(9) + '\n' + 'ie:' + isIE());