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>");
}