js判断IE6/IE7/FF

 

   if (window.XMLHttpRequest) { //Mozilla, Safari,IE7 
                alert('Mozilla, Safari,IE7 ');
                if(!window.ActiveXObject){ // Mozilla, Safari,
                        alert('Mozilla, Safari');
                  } else {
                        alert('IE7');
                   }
            } else {
             alert('IE6');
            }