javascript - HTML5-Javascript 动画不适用于 Mozilla，但适用于 Chrome

Question

我正在尝试使用 HTML5 画布为牛制作一个简单的动画。该代码适用于 Google Chrome，但不适用于 Mozilla Firefox、Safari 等。我的功能（代码）如下所示：

function animalView(objectToMove) {
  var canvas = document.getElementById('canvas'),
    context = canvas.getContext('2d');
  this.a = 0;
  (function() {
    var requestAnimationFrame = window.requestAnimationFrame ||
      window.mozRequestAnimationFrame ||
      window.webkitRequestAnimationFrame || window.msRequestAnimationFrame;
    window.requestAnimationFrame = requestAnimationFrame;
  })();
  (function drawFrame() {
    window.requestAnimationFrame(drawFrame, canvas);
    context.save();
    context.clearRect(0, 0, canvas.width, canvas.height);
    this.a += 10;
    objectToMove.tail = Math.sin( this.a );
    objectToMove.draw(context);
    context.restore();
  }());
}

我注意到this.a当回调函数调用function().