原生javascript-无间缝滚动，封装

目前支持的是竖向与横向滚动

http://lgy.1zwq.com/marScroll/

现在分析下无间缝实现的基本思路（竖向例子）：

HTML结构：

<div id="marScroll">
        <ul>
            <li>01</li>
            <li>02</li>
            <li>03</li>
            <li>04</li>
            <li>05</li>
        </ul>
</div>

CSS：

<style type="text/css">
    ul,li{padding: 0;margin: 0;}
    #marScroll{height: 60px;overflow: hidden;}
    #marScroll li{height: 20px;line-height: 20px;font-size: 14px;}
</style>

（1）首先需要判断里面的内容高度ul结构是否高于外层div#marScrolll，则才进行无间缝滚动：

       // 写在匿名函数里面，防止全局变量污染
    (function(){
        var target = document.getElementById('marScroll'),
            oUl = target.getElementsByTagName('ul')[0];
        // 内容少，则直接退出此函数
        if(oUl.offsetHeight<target.offsetHeight) return;
    })();

（2）无间缝就是内容的无限滚动展示，那么先需要复制里面的内容，然后通过外层的scrollTop++属性，用setInterval 函数进行循环执行

        target.innerHTML += target.innerHTML;
        /* 判断每次滚动的距离等于第一个ul的高度时，设置scrollTop为0，然后如此的循环操作就是无间滚动了
        ---------------------------------------------------------------------------------------------*/
        // 把功能函数抽离出来，方便调用
        var fn = function(){
            if(target.scrollTop == oUl_h){
                target.scrollTop = 0;
            }else{
                target.scrollTop++;
            }
        }
        // setInterval 循环
        var timer = setInterval(function(){
            fn();
        },30);

（3）鼠标经过此内容块时，就停止滚动

        // hover
        target.onmouseover = function(){
            clearTimeout(timer);
        }
        target.onmouseout = function(){
            timer = setInterval(function(){
                fn();
            },30);
        }

例子JS总代码：

     // 写在匿名函数里面，防止全局变量污染
    (function(){
        var target = document.getElementById('marScroll'),
            oUl = target.getElementsByTagName('ul')[0],
            oUl_h = oUl.offsetHeight;
        // 内容少，则直接退出此函数
        if(oUl_h<target.offsetHeight) return;

        target.innerHTML += target.innerHTML;

        /* 判断每次滚动的距离等于第一个ul的高度时，设置scrollTop为0，然后如此的循环操作就是无间滚动了
        ---------------------------------------------------------------------------------------------*/
        // 把功能函数抽离出来，方便调用
        var fn = function(){
            if(target.scrollTop == oUl_h){
                target.scrollTop = 0;
            }else{
                target.scrollTop++;
            }
        }
        // setInterval 循环
        var timer = setInterval(function(){
            fn();
        },30);
        // hover
        target.onmouseover = function(){
            clearTimeout(timer);
        }
        target.onmouseout = function(){
            timer = setInterval(function(){
                fn();
            },30);
        }
    })();

 已经完成了个简单的竖向无间缝，为了满足更多的需求，建议封装成可以，竖向，横向，多次调用的函数。

以下是个人的封装，线上例子：

http://lgy.1zwq.com/marScroll/

function GyMarquee(opt){
    this.opt = opt;
    if(!document.getElementById(this.opt.targetID)) return;
    this.target = document.getElementById(this.opt.targetID);
    this.dir = this.opt.dir == 'crosswise'?'crosswise':'vertical';
    this.effect = this.opt.effect == 'scroll'?'scroll':'marque';
    this.scrollHeight = this.opt.scrollHeight;
    this.init();
}
GyMarquee.prototype = {
    marquee:function(){
        var _that = this,
            direction = 'scrollTop',
            judge = this.target.scrollHeight,
            timer = null;
        if(this.dir == 'crosswise'){
            direction = 'scrollLeft';
            judge = this.itemLen*this.opt.itemWidth;
            this.targetChild.style.width = this.itemLen*this.opt.itemWidth*2 + 'px';
        }
        var doFn = function(){
            if(_that.target[direction] == judge){
                _that.target[direction] = 0;
            }
            _that.target[direction]++;
        }
        timer = setInterval(function(){
            doFn();    
        },38);
        this.target.onmouseover = function(){
            if(timer) clearTimeout(timer);
        }
        this.target.onmouseout = function(){
            timer = setInterval(function(){
                doFn();    
            },38);
        }
    },
    scrollDo:function(){
        var can = true,
            _that = this;
        this.target.onmouseover=function(){can=false};
        this.target.onmouseout=function(){can=true};
        new function (){
            var stop=_that.target.scrollTop%_that.scrollHeight==0&&!can;
            if(!stop)_that.target.scrollTop==parseInt(_that.target.scrollHeight/2)?_that.target.scrollTop=0:_that.target.scrollTop++;
            setTimeout(arguments.callee,_that.target.scrollTop%_that.scrollHeight?20:2500); 
        };
    },
    getByClassName:function(className,parent){
        var elem = [],
            node = parent != undefined&&parent.nodeType==1?parent.getElementsByTagName('*'):document.getElementsByTagName('*'),
            p = new RegExp("(^|\s)"+className+"(\s|$)");
        for(var n=0,i=node.length;n<i;n++){
            if(p.test(node[n].className)){
                elem.push(node[n]);
            }
        }
        return elem;
    },
    init:function(){
        var val = 0;
        if(this.dir =='crosswise'&&this.effect=='marque'&&this.opt.itemName!=''){
            this.itemLen = this.target.getElementsByTagName(this.opt.itemName).length;
            val = this.itemLen*this.opt.itemWidth;    
        }else{
            val = this.target.scrollHeight;
        }
        var holderHTML = this.target.innerHTML;
        this.target.innerHTML = '<div class="J_scrollInner">'+holderHTML+'</div>';
        this.targetChild = this.getByClassName('J_scrollInner',this.target)[0];
        var attr = this.dir == 'vertical'?'offsetHeight':'offsetWidth';
        if(val>this.target[attr]){
            if(this.effect == 'scroll'){
                this.scrollDo();
            }else{
                this.marquee();
            }
            this.targetChild.innerHTML += this.targetChild.innerHTML;
        }
    }
}