var btn=document.getElementById('browser');

           btn.onclick=function() {
           var exp=navigator.userAgent.toLowerCase(),brow;
              if (exp.indexOf("msie")>-1) {
                brow="ie";
              }else if(exp.indexOf("chrome")>-1){
                brow="chrome";
              }else if (exp.indexOf("opera")>-1) {
                brow="opera";
              }
              alert("您当前使用的是："+brow+"浏览器");
            }