网页添加实时显示FPS帧率

通过一下面的代码，可以让网页实时显示FPS帧率。

<script>
	jQuery(document).ready(function($){
	$('body').before('<div id="fps" style="position: fixed;right: 20px;bottom: 5px;color: #fff;font-size: 1.2px;line-height: 1;z-index:10000;padding: 5px 8px;background: #3690cf;border-radius: 5px;"></div>');
	var showFPS = (function() {
		var requestAnimationFrame = window.requestAnimationFrame || window.webkitRequestAnimationFrame || window.mozRequestAnimationFrame || window.oRequestAnimationFrame || window.msRequestAnimationFrame ||
		function(callback) {
			window.setTimeout(callback, 1000 / 60);
		};
		var e, pe, pid, fps, last, offset, step, appendFps;

		fps = 0;
		last = Date.now();
		step = function() {
			offset = Date.now() - last;
			fps += 1;
			if (offset >= 1000) {
				last += offset;
				appendFps(fps);
				fps = 0;
			}
			requestAnimationFrame(step);
		};
		appendFps = function(fps) {
			console.log(fps + ' FPS');
			$('#fps').html(fps + ' FPS');
		};
		step();
	})();
});
</script>

源代码来自网络，至于具体用处是什么，是测试网页的，还是测试浏览器性能的？暂时不知道，反倒是感觉会影响网页加载速度呢。