js 手机摇一摇

上次在玩一手游看到里面有一个摇一摇抽奖，游戏是web做的所以在网上找了些代码实现了JS摇一摇功能，

具体内容不详解，直接上码

HTML代码

<audio id="musicBox" src=""></audio>  

 JS代码

init();
		var SHAKE_THRESHOLD = 3000;
		var last_update = 0;
		var x = y = z = last_x = last_y = last_z = 0;

		function init() {
		    if (window.DeviceMotionEvent) {
		        window.addEventListener('devicemotion', deviceMotionHandler, false);
		    } else {
		        alert('not support mobile event');
		    }
		}

		function deviceMotionHandler(eventData) {
		    var acceleration = eventData.accelerationIncludingGravity;
		    var curTime = new Date().getTime();
		    if ((curTime - last_update) > 100) {
		        var diffTime = curTime - last_update;
		        last_update = curTime;
		        x = acceleration.x;
		        y = acceleration.y;
		        z = acceleration.z;
		        var speed = Math.abs(x + y + z - last_x - last_y - last_z) / diffTime * 10000;

		        if (speed > SHAKE_THRESHOLD) {
		            alert("感觉到摇动，我要发射了");
		            var media = document.getElementById("musicBox"); //获取音频控件
		            media.setAttribute("src", "imgy/shake_sound.mp3");
		            media.load(); //加载音频
		            media.play(); //播放音频 
		        }
		        last_x = x;
		        last_y = y;
		        last_z = z;
		    }
		}