JS simulation simple scroll bar effect code (with demo source code)_javascript skills

The example in this article describes how to simulate a simple scroll bar effect with JS. Share it with everyone for your reference, the details are as follows:

Use Js to simulate scroll bars. Simple mode, similar to the common scroll bar on mobile phones.

The effect is as follows:

Js code is as follows:

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;
}

Click here for the complete example codeDownload from this site.

Readers who are interested in more JavaScript-related content can check out the special topics on this site: "Summary of JavaScript switching effects and techniques", "Summary of JavaScript search algorithm techniques", "Summary of JavaScript animation special effects and techniques", "Summary of JavaScript errors and debugging skills", "Summary of JavaScript data structures and algorithm techniques", "JavaScript traversal Summary of Algorithms and Techniques" and "Summary of JavaScript Mathematical Operation Usage"

I hope this article will be helpful to everyone in JavaScript programming.