js 手機搖一搖

上次在玩一手遊看到裡面有一個搖一搖抽獎，遊戲是web做的所以在網上找了些代碼實現了JS搖一搖功能，

具體內容不詳解，直接上碼

HTML代碼

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

JS代碼

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;
   }
}