requestAnimationFrame--进度条

requestAnimationFrame

Html:
<div id="test" style="width:1px;height:17px;background:#0f0;">0%</div>
<input type="button" value="Run" id="run"/>
JS：
window.requestAnimationFrame = window.requestAnimationFrame ||
window.mozRequestAnimationFrame ||                              window.webkitRequestAnimationFrame ||                       window.msRequestAnimationFrame;
var start = null;
var ele = document.getElementById("test");
var progress = 0;

function step(timestamp) {
progress += 1;
ele.style.width = progress + "%";
ele.innerHTML=progress + "%";
if (progress < 100) {
requestAnimationFrame(step);
}
}

requestAnimationFrame(step);

document.getElementById("run").addEventListener("click", function() {
ele.style.width = "1px";
progress = 0;
requestAnimationFrame(step);
}, false);