Another way to do this without jQuery would be to use Greensock's TweenLite JS library.
Demo http://codepen.io/anon/pen/yNWwEJ
var display = document.getElementById("display");
var number = {param:0};
var duration = 1;
function count() {
TweenLite.to(number, duration, {param:"+=20", roundProps:"param",
onUpdate:update, onComplete:complete, ease:Linear.easeNone});
}
function update() {
display.innerHTML = number.param;
}
function complete() {
//alert("Complete");
}
count();