简单使用navigator.userAgent判断浏览器

<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>navigator</title>
<script type="text/javascript">
  function validB(){ 
      var u_agent = navigator.userAgent;
      var b_name = "不是想用的主流浏览器! "
      if (u_agent.indexOf("Firefox")>-1) {
          b_name="Firefox";
      }else if (u_agent.indexOf("Chrome")>-1) {
          b_name="Chrome";
      }else if (u_agent.indexOf("MSIE")>-1 && u_agent.indexOf("Trident")>-1) {
          b_name="IE(8-10)";
      };
      document.write("浏览器:"+b_name +'<br>');
      document.write("u_agent:" +u_agent);
  } 
</script>
</head>
<body>
  <form>
     <input type="button" value="查看浏览器" onclick="validB()"  >
  </form>
</body>
</html>