webApp 用js 模仿微信的摇一摇功能DeviceMotionEvent

<script type="text/javascript">
var color = new Array('#fff', '#ff0', '#f00', '#000', '#00f', '#0ff');
if(window.DeviceMotionEvent) {
var speed = 105;
var x = y = z = lastX = lastY = lastZ = 0;

var ys=1;
window.addEventListener('devicemotion', function(){
var acceleration =event.accelerationIncludingGravity;
x = acceleration.x;
y = acceleration.y;
if(Math.abs(x-lastX) > speed || Math.abs(y-lastY) > speed) {
ys+=1;
alert("你摇一摇换了桌面哦")
document.getElementById("text").innerHTML+=ys+"<br />";
document.body.style.backgroundColor = color[Math.round(Math.random()*10)%6];
}
lastX = x;
lastY = y;
}, false);
}
</script>