window.onload = function(){

        startMove();

        function startMove(){

                setInterval(function(){

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

                        odiv.style.width = parseInt(getStyle(odiv,'width')) - 2 + 'px';

                },30);

        }

        function getStyle(obj , attr){

                alert('a');          //可弹出对话框

                if (obj.currentStyle){

                        return obj.currentStyle[attr];

                }else{

                        return obj.getComputedStyle(obj,false)[attr];

                }

        }

}