JS 简易滚动条

使用Js模拟滚动条。简易模式，类似手机上常见的滚动条。

效果如下：

Js代码如下：

var scrollMoveObj = null, scrollPageY = 0, scrollY = 0;
var scrollDivList = new Array();
// obj需要添加滚动条的对象 w滚动条宽度 className滚动条样式名称
// obj元素 必须指定高度，并设置overflow:hidden;
// 如要兼容IE6 必须给obj元素 指定 overflow:hidden; 
function jsScroll(obj, w, className)
{
    if(typeof(obj) == 'string')    {
        obj = document.getElementById(obj);
    }
    //当内容未超出现在高度时，不添加滚动条    
    if(!obj || obj.scrollHeight <= obj.clientHeight || obj.clientHeight == 0) {
        return;
    }
    obj.scrollBarWidth = w||6;
    obj.style.overflow = 'hidden';
    obj.scrollBar = document.createElement('div');
    document.body.appendChild(obj.scrollBar);
    obj.scrollBarIndex = document.createElement('div');
    obj.scrollBar.appendChild(obj.scrollBarIndex);
    obj.scrollBar.style.position = 'absolute';
    obj.scrollBarIndex.style.position = 'absolute';
    obj.scrollBar.className = className || '';
    if(!className) {
        obj.scrollBar.style.backgroundColor = '#ddd';
        obj.scrollBarIndex.style.backgroundColor = '#aaa';
    }
    
    scrollDivList.push(obj);
    scrollResetSize(obj);
    
    //使用鼠标滚轮滚动
    obj.scrollBar.scrollDiv = obj;
    obj.scrollBarIndex.scrollDiv = obj;
    obj.onmousewheel = scrollMove;
    obj.scrollBar.onmousewheel = scrollMove;
    obj.scrollBarIndex.onmousewheel = scrollMove;
    
    //拖动滚动条滚动
    obj.scrollBarIndex.onmousedown = function(evt){
        evt = evt || event;
        scrollPageY = evt.clientY;
        scrollY = this.scrollDiv.scrollTop;
        isScrollMove = true;
        document.body.onselectstart = function(){return false};
        scrollMoveObj = this.scrollDiv;
        if(this.scrollDiv.scrollBar.className == '') {
            this.scrollDiv.scrollBarIndex.style.backgroundColor = '#888';
        }
        return false;
    }
}

//当页面大小发生变化时，重新计算滚动条位置
window.onresize = function(){
    for(var i=0; i<scrollDivList.length; i++) {
        scrollResetSize(scrollDivList[i]);
    }
}

//计算滚动条位置
function scrollResetSize(o) {
    if(o.scrollHeight <= o.clientHeight) {
        o.scrollTop = 0;
        o.scrollBar.style.display = 'none';
    } else {
        o.scrollBar.style.display = 'block';
    }
    var x=0, y=0;
    var p = o;
    while(p) {
        x += p.offsetLeft;
        y += p.offsetTop;
        p = p.offsetParent;
    }
    var borderTop = parseInt(o.style.borderTopWidth||0);
    var borderBottom = parseInt(o.style.borderBottomWidth||0);
    o.scrollBar.style.width = o.scrollBarWidth + 'px';
    o.scrollBar.style.height = o.clientHeight + 'px';
    o.scrollBar.style.top = y + borderTop + 'px';
    o.scrollBar.style.left = x + o.offsetWidth - o.scrollBarWidth + 'px';
    o.scrollBarIndex.style.width = o.scrollBarWidth + 'px';
    var h = o.clientHeight - (o.scrollHeight - o.clientHeight);
    //当滚动条滑块最小20个像素
    if(h < 20) {
        h = 20;
    }
    o.scrollBarHeight = h;
    o.scrollBarIndex.style.height = h + 'px';
    o.scrollBarIndex.style.left = '0px';
    setScrollPosition(o);
}

function setScrollPosition(o) {
    o.scrollBarIndex.style.top = (o.clientHeight - o.scrollBarHeight) * o.scrollTop / (o.scrollHeight - o.clientHeight) + 'px';
}

document.documentElement.onmousemove = function(evt){
    if(!scrollMoveObj)return;
    evt = evt || event;
    var per = (scrollMoveObj.scrollHeight - scrollMoveObj.clientHeight) / (scrollMoveObj.clientHeight - scrollMoveObj.scrollBarHeight)
    scrollMoveObj.scrollTop = scrollY - (scrollPageY - evt.clientY) * per;
    setScrollPosition(scrollMoveObj);
}
document.documentElement.onmouseup = function(evt){
    if(!scrollMoveObj)return;
    if(scrollMoveObj.scrollBar.className == '') {
        scrollMoveObj.scrollBarIndex.style.backgroundColor = '#aaa';
    }
    scrollMoveObj = null;
    document.body.onselectstart = function(){return true};
}

// 鼠标滚轮滚动
function scrollMove(evt){
    var div = this.scrollDiv || this;
    if(div.scrollHeight <= div.clientHeight) return true;
    evt = evt || event;
    var step = 20;
    if(evt.wheelDelta < 0) {
        if(div.scrollTop >= (div.scrollHeight - div.clientHeight)) return true;
        div.scrollTop += step;
    } else {
        if(div.scrollTop == 0) return true;
        div.scrollTop -= step;
    }
    setScrollPosition(div);
    
    return false;
}

 

实例下载：https://files.cnblogs.com/zjfree/jsScroll.rar