很多栏目中的自动转换是怎么实现的？

脚本说明:把如下代码加入<body>区域中<script language="JavaScript1.2">var slideshow_width=140 //SET IMAGE WIDTHvar slideshow_height=225 //SET IMAGE HEIGHTvar pause=3000 //SET PAUSE BETWEEN SLIDE (3000=3 seconds)var fadeimages=new Array()//SET IMAGE PATHS. Extend or contract array as neededfadeimages[0]="photo1.jpg"fadeimages[1]="photo2.jpg"fadeimages[2]="photo3.jpg"////NO need to edit beyond here/////////////var preloadedimages=new Array()for (p=0;p<fadeimages.length;p++){preloadedimages[p]=new Image()preloadedimages[p].src=fadeimages[p]}var ie4=document.all&&navigator.userAgent.indexOf("Opera")==-1var dom=document.getElementById&&navigator.userAgent.indexOf("Opera")==-1if (ie4||dom)document.write('<div style="position:relative;width:'+slideshow_width+';height:'+slideshow_height+';overflow:hidden"><div id="canvas0" style="position:absolute;width:'+slideshow_width+';height:'+slideshow_height+';top:0;filter:alpha(opacity=10);-moz-opacity:10"></div><div id="canvas1" style="position:absolute;width:'+slideshow_width+';height:'+slideshow_height+';top:0;filter:alpha(opacity=10);-moz-opacity:10"></div></div>')elsedocument.write('<img name="defaultslide" src="'+fadeimages[0]+'">')var curpos=10var degree=10var curcanvas="canvas0"var curimageindex=0var nextimageindex=1function fadepic(){if (curpos<100){curpos+=10if (tempobj.filters)tempobj.filters.alpha.opacity=curposelse if (tempobj.style.MozOpacity)tempobj.style.MozOpacity=curpos/100}else{clearInterval(dropslide)nextcanvas=(curcanvas=="canvas0")? "canvas0" : "canvas1"tempobj=ie4? eval("document.all."+nextcanvas) : document.getElementById(nextcanvas)tempobj.innerHTML='<img src="'+fadeimages[nextimageindex]+'">'nextimageindex=(nextimageindex<fadeimages.length-1)? nextimageindex+1 : 0setTimeout("rotateimage()",pause)}}function rotateimage(){if (ie4||dom){resetit(curcanvas)var crossobj=tempobj=ie4? eval("document.all."+curcanvas) : document.getElementById(curcanvas)crossobj.style.zIndex++var temp='setInterval("fadepic()",50)'dropslide=eval(temp)curcanvas=(curcanvas=="canvas0")? "canvas1" : "canvas0"}elsedocument.images.defaultslide.src=fadeimages[curimageindex]curimageindex=(curimageindex<fadeimages.length-1)? curimageindex+1 : 0}function resetit(what){curpos=10var crossobj=ie4? eval("document.all."+what) : document.getElementById(what)if (crossobj.filters)crossobj.filters.alpha.opacity=curposelse if (crossobj.style.MozOpacity)crossobj.style.MozOpacity=curpos/100}function startit(){var crossobj=ie4? eval("document.all."+curcanvas) : document.getElementById(curcanvas)crossobj.innerHTML='<img src="'+fadeimages[curimageindex]+'">'rotateimage()}if (ie4||dom)window.onload=startitelsesetInterval("rotateimage()",pause)</script>

很多栏目中的自动转换是怎么实现的？

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