<script?type="text/javascript">
?var?top1?=?document.getElementById('top');
?var?con1?=?document.getElementById('con1');
?var?con2?=?document.getElementById('con2');
?var?time?=?50;
?top1.scrollTop?=?0;
?con2.innerHTML?=?con1.innerHTML;
?function?start(){
????if(top1.scrollTop?>=?con1.scrollHeight){
????????top1.scrollTop?=?0;
????????}else{
????????top1.scrollTop?++;????
????????????}
????}
var?iTime?=?setInterval("start()",time);
top1.onmouseover?=?function(){
????clearInterval(iTime);
????}
top1.onmouseout?=?function(){
????iTime?=?setInterval("start()",time);
????}
</script>

上面這段代碼能實現滾動。

下面的代碼幾乎一樣的，就是var?top?=?document.getElementById('top');不同。

下面這段代碼不能實現滾動，沒有反應

這到底有什么不同嗎？就是變量名稱不同

其他HTML ，CSS都一樣的；

為什么這條語句會無效？

var?top?=?document.getElementById('top');

最后反復實驗了，當var top = document.getElementById('top');
的時候，不能實現滾動，這是為什么呢

<script?type="text/javascript">
?var?top?=?document.getElementById('top');
?var?con1?=?document.getElementById('con1');
?var?con2?=?document.getElementById('con2');
?var?time?=?50;
?top.scrollTop?=?0;
?con2.innerHTML?=?con1.innerHTML;
?function?start(){
????if(top.scrollTop?>=?con1.scrollHeight){
????????top.scrollTop?=?0;
????????}else{
????????top.scrollTop?++;????
????????????}
????}
var?iTime?=?setInterval("start()",time);
top.onmouseover?=?function(){
????clearInterval(iTime);
????}
top.onmouseout?=?function(){
????iTime?=?setInterval("start()",time);
????}
</script>