js 判断是手机请求还是pc请求

function getRequest(){
    var system ={
win : false,
mac : false,
xll : false
};
//检测平台
var p = navigator.platform;
system.win = p.indexOf("Win") == 0;
system.mac = p.indexOf("Mac") == 0;
system.x11 = (p == "X11") || (p.indexOf("Linux") == 0);

if(system.win||system.mac||system.xll){
alert("web");//此请求时电脑访问
}else{
alert("phone");//此请求时手机访问
}
    }