使图片永远在页面顶端的特效代码

<div id=dd style="Z-INDEX: 1; WIDTH: 100px; POSITION: absolute; HEIGHT: 132px"> <a href="http://www.downcodes.com/"><img src="/img/200406301.jpg" width="236" height="236" border="0" alt="马到成功！"></a></div> <script language=JavaScript> <!-- Begin //more javascript from http://www.downcodes.com var xPos = 20; // 起始横向位置(从左算起，单位象素) var yPos = document.body.clientHeight; // 页面本身高度 var step = 1; var delay = 30; // 速度，值越大速度越慢 var height = 0; var Hoffset = 0; var Woffset = 0; var yon = 0; var xon = 0; var pause = true; var interval; dd.style.top = yPos; function changePos() { width = document.body.clientWidth; // 判断浏览器窗口的宽度 height = document.body.clientHeight; // 判断浏览器窗口的高度 Hoffset = dd.offsetHeight; Woffset = dd.offsetWidth; dd.style.left = xPos + document.body.scrollLeft; dd.style.top = yPos + document.body.scrollTop; if (yon) { yPos = yPos + step; } else { yPos = yPos - step; } if (yPos < 0) { yon = 1; yPos = 0; } if (yPos >= (height - Hoffset)) { yon = 0; yPos = (height - Hoffset); } if (xon) { xPos = xPos + step; } else { xPos = xPos - step; } if (xPos < 0) { xon = 1; xPos = 0; } if (xPos >= (width - Woffset)) { xon = 0; xPos = (width - Woffset); } } function start() { dd.visibility = "visible"; interval = setInterval('changePos()', delay); } function pause_resume() { if(pause) {clearInterval(interval);pause = false;} else {interval = setInterval('changePos()',delay);pause = true;} } start(); // End --> </script>