js achieve smooth animation by window.requestAnimationFrame

Write a browser compatible with a variety of global method

window.requestAnimaFrame = (function(){
	return window.requestAnimationFrame ||
		   window.webkitRequestAnimationFrame ||
		   window.mozRequestAnimationFrame ||
		   window.oRequestAnimationFrame ||
		   window.msRequestAnimationFrame ||
		   function(callback){
				setTimeout(callback, 1000 / 60);
			};
)();

Call the global method

//调用全局方法
function startAnimation(){
	requestAnimaFrame(startAnimation);
}
//requestAnimationFrame 只能按照浏览器刷新机制执行一次， 
//所以需要实现动画需要像setTimeout使用方法一样，在自己的方法中调用自己
startAnimation();