javascript无缝滚动2

以更少的代码实现相同的效果应该是我们写程序的究极目标，当然可读性不能丢。在第一部分最后一个运行框，我已经做了这样的探索。不过换汤不换药，还是来来回回在scrollTop/scrollLeft与offsetTop/offsetLeft上做文章。总的思路基本是这样，让某个元素整体向某个方向移动，这样它里面的内容（图片或文字）就跟着移动，当元素移动到某一个距离后就回到原点。为了防止内容移着移着就没有了，我们需要两套相同的内容。在第一部分，第二套内容是动态生成的，并复制到另一个兄弟元素中，这在水平滚动时，我们需要花一些周折来让所有内容水平排列在一起。我就想，如果把第二套内容直接加在相同的元素是否效果会更好呢？起码CSS也少写一点。用scrollTop/scrollLeft实现滚动，还有一个缺点，它对父容器的宽度与高度有严格的规定的。比如我们想上下滚动图片，ul作为容器，li的图片为滚动内容，那么ul的高至少为图片的高的两倍（我们假设每张图片的尺寸都是相等的），否则就动不了。鉴此，我开发了新一代的无缝滚动函数。

<ul id="marquee">
  <li>
    <a href="http://www.cnblogs.com/rubylouvre/"><img src="o_s017.jpg" alt="无缝滚动"/></a>
    <a href="http://www.cnblogs.com/rubylouvre/"><img src="o_s018.jpg" alt="无缝滚动"/></a>
    <a href="http://www.cnblogs.com/rubylouvre/"><img src="o_s019.jpg" alt="无缝滚动"/></a>
    <a href="http://www.cnblogs.com/rubylouvre/"><img src="o_s020.jpg" alt="无缝滚动"/></a>
    <a href="http://www.cnblogs.com/rubylouvre/"><img src="o_s021.jpg" alt="无缝滚动"/></a>
    <a href="http://www.cnblogs.com/rubylouvre/"><img src="o_s022.jpg" alt="无缝滚动"/></a>
    <a href="http://www.cnblogs.com/rubylouvre/"><img src="o_s023.jpg" alt="无缝滚动"/></a>
  </li>
</ul>

#marquee ,#marquee li {
  padding:0;
  margin:0;
}
#marquee {
  position:relative;
  list-style:none;
  height:150px;
  width:200px;
  overflow:hidden;
  border:10px solid #369;
}
#marquee li {
  position:absolute;
}
#marquee img {
  display:block;
  border:0;
}

var Marquee = function(id){
  try{document.execCommand("BackgroundImageCache", false, true);}catch(e){};
  var container = document.getElementById(id),
  slide = container.getElementsByTagName("li")[0],
  speed = arguments[1] || 10,
  delta = 0,//当前滚动的位置
  critical = slide.offsetHeight;//临界值
  slide.innerHTML += slide.innerHTML;
  var rolling = function(){
    delta == -critical ? delta = 0 : delta--;
    slide.style.top = delta + "px";
  }
  var timer = setInterval(rolling,speed)//设置定时器
  container.onmouseover=function() {clearInterval(timer)}//鼠标移到marquee上时，清除定时器，停止滚动
  container.onmouseout=function() {timer=setInterval(rolling,speed)}//鼠标移开时重设定时器
}
window.onload = function(){
  Marquee("marquee");
}

<!doctype html>
<title>javascript无缝滚动  by 司徒正美</title>
<meta charset="utf-8"/>
<meta name="keywords" content="javascript无缝滚动 by 司徒正美" />
<meta name="description" content="javascript无缝滚动  by 司徒正美" />
<base href="http://images.cnblogs.com/cnblogs_com/rubylouvre/199042/">
<style type="text/css">
  h1 {
    font:400 16px/1 "Microsoft YaHei",KaiTi_GB2312,SimSun
  }
  #marquee ,#marquee li {
    padding:0;
    margin:0;
  }
  #marquee {
    position:relative;
    list-style:none;
    height:150px;
    width:200px;
    overflow:hidden;
    border:10px solid #369;
  }
  #marquee li {
    position:absolute;
  }
  #marquee img {
    display:block;
    border:0;
  }
</style>
<script type="text/javascript">
  var Marquee = function(id){
    try{document.execCommand("BackgroundImageCache", false, true);}catch(e){};
    var container = document.getElementById(id),
    slide = container.getElementsByTagName("li")[0],
    speed = arguments[1] || 10,
    delta = 0,//当前滚动的位置
    critical = slide.offsetHeight;//临界点
    slide.innerHTML += slide.innerHTML;
    var rolling = function(){
      delta == -critical ? delta = 0 : delta--;
      slide.style.top = delta + "px";
    }
    var timer = setInterval(rolling,speed)//设置定时器
    container.onmouseover=function() {clearInterval(timer)}//鼠标移到marquee上时，清除定时器，停止滚动
    container.onmouseout=function() {timer=setInterval(rolling,speed)}//鼠标移开时重设定时器
  }
  window.onload = function(){
    Marquee("marquee");
  }
</script>
<h1>javascript无缝滚动(向上滚动) by 司徒正美</h1>
<base href="http://images.cnblogs.com/cnblogs_com/rubylouvre/199042/">
<ul id="marquee">
  <li>
    <a href="http://www.cnblogs.com/rubylouvre/"><img src="o_s017.jpg" alt="无缝滚动 by 司徒正美"/></a>
    <a href="http://www.cnblogs.com/rubylouvre/"><img src="o_s018.jpg" alt="无缝滚动 by 司徒正美"/></a>
    <a href="http://www.cnblogs.com/rubylouvre/"><img src="o_s019.jpg" alt="无缝滚动 by 司徒正美"/></a>
    <a href="http://www.cnblogs.com/rubylouvre/"><img src="o_s020.jpg" alt="无缝滚动 by 司徒正美"/></a>
    <a href="http://www.cnblogs.com/rubylouvre/"><img src="o_s021.jpg" alt="无缝滚动 by 司徒正美"/></a>
    <a href="http://www.cnblogs.com/rubylouvre/"><img src="o_s022.jpg" alt="无缝滚动 by 司徒正美"/></a>
    <a href="http://www.cnblogs.com/rubylouvre/"><img src="o_s023.jpg" alt="无缝滚动 by 司徒正美"/></a>
  </li>
</ul>

向下滚动也很容易，只不过一开始把它定位到第一套内容与第二套内容之间，也就是slide.offsetHeight，不过我们需要把它改成负数让向整体向下移动，然后再慢慢向上移动。

<!doctype html>
<title>javascript无缝滚动  by 司徒正美</title>
<meta charset="utf-8"/>
<meta name="keywords" content="javascript无缝滚动 by 司徒正美" />
<meta name="description" content="javascript无缝滚动  by 司徒正美" />
<base href="http://images.cnblogs.com/cnblogs_com/rubylouvre/199042/">
<style type="text/css">
  h1 {
    font:400 16px/1 "Microsoft YaHei",KaiTi_GB2312,SimSun
  }
  #marquee ,#marquee li {
    padding:0;
    margin:0;
  }
  #marquee {
    position:relative;
    list-style:none;
    height:150px;
    width:200px;
    overflow:hidden;
    border:10px solid #B45B3E;
  }
  #marquee li {
    position:absolute;
  }
  #marquee img {
    display:block;
    border:0;
  }
</style>
<script type="text/javascript">
  var Marquee = function(id){
    try{document.execCommand("BackgroundImageCache", false, true);}catch(e){};
    var container = document.getElementById(id),
    slide = container.getElementsByTagName("li")[0],
    speed = arguments[1] || 10,
    critical = slide.offsetHeight,//临界值
    delta = -critical;
    slide.innerHTML += slide.innerHTML;
    var rolling = function(){
      delta == 0 ? delta = -critical : delta++;
      slide.style.top = delta + "px";
    }
    var timer = setInterval(rolling,speed)//设置定时器
    container.onmouseover=function() {clearInterval(timer)}//鼠标移到marquee上时，清除定时器，停止滚动
    container.onmouseout=function() {timer=setInterval(rolling,speed)}//鼠标移开时重设定时器
  }
  window.onload = function(){
    Marquee("marquee");
  }
</script>
<h1>javascript无缝滚动(向下滚动) by 司徒正美</h1>
<base href="http://images.cnblogs.com/cnblogs_com/rubylouvre/199042/">
<ul id="marquee">
  <li>
    <a href="http://www.cnblogs.com/rubylouvre/"><img src="o_s017.jpg" alt="无缝滚动"/></a>
    <a href="http://www.cnblogs.com/rubylouvre/"><img src="o_s018.jpg" alt="无缝滚动"/></a>
    <a href="http://www.cnblogs.com/rubylouvre/"><img src="o_s019.jpg" alt="无缝滚动"/></a>
    <a href="http://www.cnblogs.com/rubylouvre/"><img src="o_s020.jpg" alt="无缝滚动"/></a>
    <a href="http://www.cnblogs.com/rubylouvre/"><img src="o_s021.jpg" alt="无缝滚动"/></a>
    <a href="http://www.cnblogs.com/rubylouvre/"><img src="o_s022.jpg" alt="无缝滚动"/></a>
    <a href="http://www.cnblogs.com/rubylouvre/"><img src="o_s023.jpg" alt="无缝滚动"/></a>
  </li>
</ul>

实现水平移动也比第一部分容易，结构层完全不用改动，表现层也改动很少。

#marquee ,#marquee li {
  padding:0;
  margin:0;
}
#marquee {
  position:relative;
  list-style:none;
  height:150px;
  width:200px;
  overflow:hidden;
  border:10px solid #B45B3E;
}
#marquee li {
  position:absolute;
  width:1000%;/*★★新增加★★*/
}
#marquee a {
  float:left;/*★★新增加★★*/
}
#marquee img {
  display:block;
  border:0;
}

难点是如何获取那个临界值，也就是夹在第一套内容与第二个套内容之间的那个位置。由于第二套内容我们并没有外套一个元素，因此我们需要从滚动对象下手。滚动对象都是a元素，我们需要计算出第二套内容的第一个a元素到达父元素左边的距离。这个值就是我们要求的临界值。明白这点，就轻松了。

  //*************略********* 
  slide.innerHTML += slide.innerHTML;
  var item  = slide.getElementsByTagName("a"),
  critical = item[item.length/2].offsetLeft,//临界值
//*************略********* 

<!doctype html>
<title>javascript无缝滚动  by 司徒正美</title>
<meta charset="utf-8"/>
<meta name="keywords" content="javascript无缝滚动 by 司徒正美" />
<meta name="description" content="javascript无缝滚动  by 司徒正美" />
<base href="http://images.cnblogs.com/cnblogs_com/rubylouvre/199042/">
<style type="text/css">
  h1 {
    font:400 16px/1 "Microsoft YaHei",KaiTi_GB2312,SimSun
  }
  #marquee ,#marquee li {
    padding:0;
    margin:0;
  }
  #marquee {
    position:relative;
    list-style:none;
    height:150px;
    width:200px;
    overflow:hidden;
    border:10px solid #8080C0;
  }
  #marquee li {
    position:absolute;
    width:1000%;/*新增加*/
  }
  #marquee a {
    float:left;/*新增加*/
  }
  #marquee img {
    display:block;
    border:0;
  }
</style>
<script type="text/javascript">
  var Marquee = function(id){
    try{document.execCommand("BackgroundImageCache", false, true);}catch(e){};
    var container = document.getElementById(id),
    slide = container.getElementsByTagName("li")[0],
    speed = arguments[1] || 10;
    slide.innerHTML += slide.innerHTML;
    var item  = slide.getElementsByTagName("a"),
    critical = item[item.length/2].offsetLeft,//临界值
    delta = 0;
    var rolling = function(){
      delta == -critical ? delta = 0 : delta--;
      slide.style.left = delta + "px";
    }
    var timer = setInterval(rolling,speed)//设置定时器
    container.onmouseover=function() {clearInterval(timer)}//鼠标移到marquee上时，清除定时器，停止滚动
    container.onmouseout=function() {timer=setInterval(rolling,speed)}//鼠标移开时重设定时器
  }
  window.onload = function(){
    Marquee("marquee");
  }
</script>
<h1>javascript无缝滚动(向左滚动) by 司徒正美</h1>
<base href="http://images.cnblogs.com/cnblogs_com/rubylouvre/199042/">
<ul id="marquee">
  <li>
    <a href="http://www.cnblogs.com/rubylouvre/"><img src="o_s017.jpg" alt="无缝滚动"/></a>
    <a href="http://www.cnblogs.com/rubylouvre/"><img src="o_s018.jpg" alt="无缝滚动"/></a>
    <a href="http://www.cnblogs.com/rubylouvre/"><img src="o_s019.jpg" alt="无缝滚动"/></a>
    <a href="http://www.cnblogs.com/rubylouvre/"><img src="o_s020.jpg" alt="无缝滚动"/></a>
    <a href="http://www.cnblogs.com/rubylouvre/"><img src="o_s021.jpg" alt="无缝滚动"/></a>
    <a href="http://www.cnblogs.com/rubylouvre/"><img src="o_s022.jpg" alt="无缝滚动"/></a>
    <a href="http://www.cnblogs.com/rubylouvre/"><img src="o_s023.jpg" alt="无缝滚动"/></a>
  </li>
</ul>

下面是向右滚动，由于都是不足20行的脚本，应该一看源码就明白，不详述了。

<!doctype html>
<title>javascript无缝滚动  by 司徒正美</title>
<meta charset="utf-8"/>
<meta name="keywords" content="javascript无缝滚动 by 司徒正美" />
<meta name="description" content="javascript无缝滚动  by 司徒正美" />
<base href="http://images.cnblogs.com/cnblogs_com/rubylouvre/199042/">
<style type="text/css">
  h1 {
    font:400 16px/1 "Microsoft YaHei",KaiTi_GB2312,SimSun
  }
  #marquee ,#marquee li {
    padding:0;
    margin:0;
  }
  #marquee {
    position:relative;
    list-style:none;
    height:150px;
    width:200px;
    overflow:hidden;
    border:10px solid #6cc;
  }
  #marquee li {
    position:absolute;
    width:1000%;
  }
  #marquee a {
    float:left;
  }
  #marquee img {
    display:block;
    border:0;
  }
</style>
<script type="text/javascript">
  var Marquee = function(id){
    try{document.execCommand("BackgroundImageCache", false, true);}catch(e){};
    var container = document.getElementById(id),
    slide = container.getElementsByTagName("li")[0],
    speed = arguments[1] || 10;
    slide.innerHTML += slide.innerHTML;
    var item  = slide.getElementsByTagName("a"),//临界点
    critical = item[item.length/2].offsetLeft,
    delta = -critical;
    var rolling = function(){
      delta == 0 ? delta = -critical : delta++;
      slide.style.left = delta + "px";
    }
    var timer = setInterval(rolling,speed)//设置定时器
    container.onmouseover=function() {clearInterval(timer)}//鼠标移到marquee上时，清除定时器，停止滚动
    container.onmouseout=function() {timer=setInterval(rolling,speed)}//鼠标移开时重设定时器
  }
  window.onload = function(){
    Marquee("marquee");
  }
</script>
<h1>javascript无缝滚动(向右滚动) by 司徒正美</h1>
<base href="http://images.cnblogs.com/cnblogs_com/rubylouvre/199042/">
<ul id="marquee">
  <li>
    <a href="http://www.cnblogs.com/rubylouvre/"><img src="o_s017.jpg" alt="无缝滚动"/></a>
    <a href="http://www.cnblogs.com/rubylouvre/"><img src="o_s018.jpg" alt="无缝滚动"/></a>
    <a href="http://www.cnblogs.com/rubylouvre/"><img src="o_s019.jpg" alt="无缝滚动"/></a>
    <a href="http://www.cnblogs.com/rubylouvre/"><img src="o_s020.jpg" alt="无缝滚动"/></a>
    <a href="http://www.cnblogs.com/rubylouvre/"><img src="o_s021.jpg" alt="无缝滚动"/></a>
    <a href="http://www.cnblogs.com/rubylouvre/"><img src="o_s022.jpg" alt="无缝滚动"/></a>
    <a href="http://www.cnblogs.com/rubylouvre/"><img src="o_s023.jpg" alt="无缝滚动"/></a>
  </li>
</ul>

我们可以把上面四个函数合并成一个函数，结构层与表现层参照向上滚动。

var Marquee = function(id){
  try{document.execCommand("BackgroundImageCache", false, true);}catch(e){};
  var container = document.getElementById(id),
  slide = container.getElementsByTagName("li")[0],
  options = arguments[1] || {},
  speed = options.speed || 10,
  direction = options.direction || "left";
  slide.innerHTML += slide.innerHTML;
  var item  = slide.getElementsByTagName("a"),
  critical,delta,rolling,field;
  if(direction == "left" || direction == "right"){
    slide.style.cssText = "width:1000%";
    for(var i=0 ,l=item.length; i<l;i++){
      item[i].style.cssText = "float:left";
    }
    field = "left";
    critical = item[item.length/2].offsetLeft;
  }else if(direction == "up" || direction == "down"){
    field = "top";
    critical = item[item.length/2].offsetTop;
  }
  if(direction == "up" || direction == "left"){
    delta = 0;
    rolling = function(){
      delta == -critical ? delta = 0 : delta--;
      slide.style[field]  = delta + "px";
    }
  }else if(direction == "down" || direction == "right"){
    delta = -critical;
    rolling = function(){
      delta == 0 ? delta = -critical : delta++;
      slide.style[field] = delta + "px";
    }
  }
  var timer = setInterval(rolling,speed)//设置定时器
  container.onmouseover=function() {clearInterval(timer)}//鼠标移到marquee上时，清除定时器，停止滚动
  container.onmouseout=function() {timer=setInterval(rolling,speed)}//鼠标移开时重设定时器
}