[caetus]

function animate (obj) {
var start = +new Date();
  var timer = setInterval(function(){
        var progress = (+new Date() - start) obj.delay// время анимации
        
        if(progress > 1) progress = 1;
        obj.fn(progress);
        if(progress == 1) clearInterval(timer):
}, 20)

}


window.onload = animate({
delay: 500,
element: document.getElementById('div'),
fn: function (progress) {

this.element.style.top = 50 * progress + 'px';
}