返回顶部javascript代码2

by kujian

HTML

<div id="gotop" class="fixed">
返回顶部
</div>
<div class="placeholder"></div>

CSS

.fixed{ position:fixed; bottom:100px; width:20px; right:100px; height:80px; font-size:12px; cursor:pointer; background-color:#ccc; opacity:0; filter: alpha(opacity=0); z-index:999;}
.placeholder{ height:2000px;}

JavaScript

var tool = {    
    //此方法为了避免在 ms 段时间内，多次执行func。常用 resize、scoll、mousemove等连续性事件中
    buffer: function(func, ms, context){
        var buffer;
        return  function(){
           if(buffer) return;
            
           buffer = setTimeout(function(){
                func.call(this);
                buffer = undefined;
            },ms);
        };
    },
     
    /*读取或设置元素的透明度*/
    opacity: function(elem, val){   
        var setting = arguments.length > 1;
        if("opacity" in elem.style){//elem.style["opacity"] 读取不到CSS class中的值
            return setting ? elem.style["opacity"] = val : elem.style["opacity"];
        }else{ 
            if(elem.filters && elem.filters.alpha) {
                return setting ? elem.filters.alpha["opacity"] = val*100 : elem.filters.alpha["opacity"]/100;
            }
        }
    },
     
    //获取或设置文档对象的scrollTop
    //function([val])
    documentScrollTop: function(val){
        var elem = document; 
        return (val!== undefined) ? 
            elem.documentElement.scrollTop = elem.body.scrollTop = val :
            Math.max(elem.documentElement.scrollTop, elem.body.scrollTop);
                 
    }
};
//动画效果
var effect = {  
    //淡入
    fadein: function (elem){
        var val = 0;
        var interval = 25;
         
        setTimeout(function(){
            val += 0.1;
            if(val>1){
                tool.opacity(elem, 1)
                return;
            }else {
                tool.opacity(elem, val)
                setTimeout(arguments.callee, interval);
            }
        },interval);
         
    },
     
    //淡出
    fadeout: function (elem){
        var val = 1;
        var interval = 25;
         
        setTimeout(function(){
            val -= 0.1; 
             
            if(val < 0){
                tool.opacity(elem, 0)
                return; 
            }else {
                tool.opacity(elem,val) ;
                setTimeout(arguments.callee, interval);
            }
    ...