Common effect implementation: return to top (combined with fade-in, fade-out, slow-down scrolling)_javascript skills

<script> <br>var tool = { <br>//This method is to avoid executing func multiple times within a period of ms. <br>buffer: function(func, ms, context){ <br>var buffer; <br>return function(){ <br>if(buffer) return; <br>buffer = setTimeout(function(){ <br>func.call(this) <br>buffer = undefined; <br>},ms); <br>}; <br>}, <br>/*Read Or set the transparency of the element*/ <br>opacity: function(elem, val){ <br>var setting = arguments.length > 1; <br>if("opacity" in elem.style){//elem. style["opacity"] cannot read the value in CSS class <br>return setting ? elem.style["opacity"] = val : elem.style["opacity"]; <br>}else{ <br> if(elem.filters && elem.filters.alpha) { <br>return setting ? elem.filters.alpha["opacity"] = val*100 : elem.filters.alpha["opacity"]/100; <br> } <br>} <br>}, <br>//Get or set the scrollTop of the document object <br>//function([val]) <br>documentScrollTop: function(val){ <br>var elem = document ; <br>return (val!== undefined) ? <br>elem.documentElement.scrollTop = elem.body.scrollTop = val : <br>Math.max(elem.documentElement.scrollTop, elem.body.scrollTop); <br>} <br>}; <br>//Animation effect<br>var effect = { <br>//Fade in<br>fadein: function (elem){ <br>var val = 0; <br> var interval = 25; <br>setTimeout(function(){ <br>val = 0.1; <br>if(val>1){ <br>tool.opacity(elem, 1) <br>return; <br> }else { <br>tool.opacity(elem, val) <br>setTimeout(arguments.callee, interval); <br>} <br>},interval); <br>}, <br>//fade out<br>fadeout: function (elem){ <br>var val = 1; <br>var interval = 25; <br>setTimeout(function(){ <br>val -= 0.1; <br>if(val < 0){ <BR>tool.opacity(elem, 0) <BR>return; <BR>}else { <BR>tool.opacity(elem,val); <BR>setTimeout(arguments.callee, interval); <BR>} <BR>},interval); <BR>}, <BR>//Slow down the moving scroll bar<BR>move: function(scrollTop){ <BR>setTimeout(function(){ <BR>scrollTop = Math .floor((scrollTop * 0.65)); <BR>tool.documentScrollTop(scrollTop); <BR>if(scrollTop !=0 ){ <BR>setTimeout(arguments.callee, 25); <BR>} <BR> },25); <BR>} <BR>}; <BR>//Main program<BR>(function(){//gotop <BR>var visible = false; <BR>var elem = document.getElementById( "gotop"); <BR>function onscroll(){ <BR>var scrollTop = tool.documentScrollTop(); <BR>if(scrollTop > 0){ <br>if(!visible){ <br>effect. fadein(elem) <br>visible = true; <br>} <br>}else{ <br>if(visible){ <br>effect.fadeout(elem); <br>visible = false; <br>} <br>} <br>} <br>function onclick(){ <br>var scrollTop = tool.documentScrollTop(); <br>effect.move(scrollTop); <br>} <br>elem.onclick = onclick ; <br>window.onscroll = tool.buffer(onscroll, 200, this); <br>})(); <br></script>

Compatibility and bugs related issues:
1 opacity: function(elem, val){
　if(val){//Using this judgment method will cause BUG when passing 0 or empty string.
2: document.documentElement.scrollTop chrome cannot get the value.
3: elem.style.opacity cannot read the value defined in CSS Class.
4: IE6 does not support fixed positioning, although absolute simulation can be used. However, many websites have downgraded it.