js使用userAgent判断浏览器信息

function validB(){   var u_agent = navigator.userAgent;   var B_name="Failed to identify the browser";   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("B_name:"+B_name+"<br>");    document.write("u_agent:"+u_agent+"<br>"); }