javascript实现的图片预览功能

<script>/*Thumbnail image viewer-?Dynamic Drive (www.dynamicdrive.com)For full source code, usage terms, and 100's more DHTML scripts, visit http://dynamicdrive.com*/function enlarge(which,e){//Render image code for IE 4+if (document.all){if (showimage.style.visibility=="hidden"){showimage.style.left=document.body.scrollLeft+event.clientXshowimage.style.top=document.body.scrollTop+event.clientYshowimage.innerHTML='<img src="'+which+'">'showimage.style.visibility="visible"}elseshowimage.style.visibility="hidden"return false}//Render image code for NS 4else if (document.layers){if (document.showimage.visibility=="hide"){document.showimage.document.write('<a href="#" rel="external nofollow" onMouseover="drag_dropns(showimage)"><img src="'+which+'" border=0></a>')document.showimage.document.close()document.showimage.left=e.xdocument.showimage.top=e.ydocument.showimage.visibility="show"}elsedocument.showimage.visibility="hide"return false}//if NOT IE 4+ or NS 4, simply display image in full browser windowelsereturn true}</script><script language="JavaScript1.2">//By Dynamicdrive.com//drag drop function for NS 4/////////////////////////////////////var nsxvar nsyvar nstempfunction drag_dropns(name){temp=eval(name)temp.captureEvents(Event.MOUSEDOWN | Event.MOUSEUP)temp.onmousedown=gonstemp.onmousemove=dragnstemp.onmouseup=stopns}function gons(e){temp.captureEvents(Event.MOUSEMOVE)nsx=e.xnsy=e.y}function dragns(e){temp.moveBy(e.x-nsx,e.y-nsy)return false}function stopns(){temp.releaseEvents(Event.MOUSEMOVE)}//drag drop function for IE 4+/////////////////////////////////////var dragapproved=falsefunction drag_dropie(){if (dragapproved==true){document.all.showimage.style.pixelLeft=tempx+event.clientX-iexdocument.all.showimage.style.pixelTop=tempy+event.clientY-ieyreturn false}}function initializedragie(){if (event.srcElement.parentElement.id=="showimage"){iex=event.clientXiey=event.clientYtempx=showimage.style.pixelLefttempy=showimage.style.pixelTopdragapproved=truedocument.onmousemove=drag_dropie}}if (document.all){document.onmousedown=initializedragiedocument.onmouseup=new Function("dragapproved=false")}</script>