JS模拟简易滚动条效果代码(附demo源码)

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;}