js- js访问html

 <img id="img1" src="1.jpg" onmouseover="2.jpg" onmouseout="3.jpg" title="鼠标放在上面，变成2，鼠标移开变成3" />

和上面是以个效果

 <img id="img1" src="1.jpg" title="鼠标放在上面，变成2，鼠标移开变成3" />

<script language="javascript" type="text/javascript">
        var a = document.getElementById("img1");
        img1.onmouseover = over;
        img1.onmouseout = out;
        function over() {
            this.src = "2.jpg";
        }
        function out() {
            this.src = "3.jpg";
        }

    </script>