js 判断当前是手机还是电脑

<script type="text/javascript">
    var system ={};
       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){//如果是电脑跳转到
       alert("电脑")
       }else{  //如果是手机,跳转到
       alert("手机")
       }
</script>