spectrum learns to dig

http://jsdo.it/spectrum/rG9b setInterval 로 bpm 카운터를 만들어봤더니 시간이 말도 안되게 안맞아서 requestAnimFrame을 사용해 오차를 측정해보았다. var p = {     frameRate : 60,     fps : document.querySelector('#fps'),     deltaTime : 0,     onLoad : function() { fps.onclick=p.onClick;     },     onClick : function() { p.setDelta(); p.animationLoop();     },     setDelta : function() { p.deltaTime = +(new Date());     },     animationLoop : function() { var currentTime = +(new Date()); p.fps.innerHTML= (currentTime - p.deltaTime) +'msec/frame in 60frames'; p.setDelta(); requestAnimFrame(p.animationLoop);     } }; window.onload=p.onLoad; window.requestAnimFrame = (function(callback) {     return window.requestAnimationFrame || window.webkitRequestAnimationFrame || window.mozRequestAnimationFrame || window.oRequestAnimationFrame || window.msRequestAnimationFrame || ...