window.onload = function() {

        var div1 = document.getElementById('div1');

        div1.onmouseover = function(){

             startMove(this,400);

        }

        div1.onmouseout = function(){

             startMove(this,200);

        }

        function startMove(obj, iTarget) {

            clearInterval(obj.timer);

            obj.timer = setInterval(

                function() {

                    var speed = (iTarget-obj.offsetHeight)/3;

                    obj.style.height = obj.offsetHeight + speed + 'px';

                    obj.style.width = obj.offsetWidth + speed + 'px';                

                }, 30)

        };

    }