jquery 判断当前设备是PC端还是移动端？

$(function(){
var system = {
win: false,
mac: false,
xll: false,
ipad: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);
    system.ipad = (navigator.userAgent.match(/iPad/i) != null)?true:false;
if (system.win || system.mac || system.xll ||system.ipad) {
    } else {
       some code;
    }
})