Rigged Wiki group browsing script thing

<script>
var rowHoverBG;
var selectedGroup = null;
var selectedMatch = null;
var groupShow, matchShow;
window.addEventListener("load",onLoad,true);
function onLoad(){
  document.getElementById("groupBrowseControls").style.display = "";
  rowHoverBG = document.getElementById("groupBrowseControls").dataset.rowhovercolor;
  groupShow = document.getElementById("groupShow");
  matchShow = document.getElementById("matchShow");
  groupSel.addEventListener("change",selchange,true);
  hideAll();
  window.removeEventListener("load",onLoad,true);
}
function hideAll(){
  var groupDivs = document.getElementsByClassName("groupDiv");
  var groupSel = document.getElementById("groupSel");
  for(var i = 0; i<groupDivs.length; ++i){
    groupDivs[i].style.display="";
    groupSel.add(new Option("Group "+groupDivs[i].id.substr(5),groupDivs[i].id),null);
  }
  var groupTables = document.getElementsByClassName("groupTable");
  for(i = 0; i<groupTables.length; ++i){
    groupTables[i].removeEventListener("mouseover",teamMouseOver);
    groupTables[i].addEventListener("mouseover",teamMouseOver);
  }
  hideMatches();
  matchShow.style.display = "";
  groupSel.addEventListener("change",selchange,true);
  groupShow.innerHTML = "All Groups";
  groupShow.removeEventListener("click",hideAll,true);
  groupShow.addEventListener("click",showAll,true);
}
function showAll(){
  var groupDivs = document.getElementsByClassName("groupDiv");
  var groupSel = document.getElementById("groupSel");
  for(var i = 0; i<groupDivs.length; ++i){
    groupDivs[i].style.display="";
  }
  selectedGroup = null;
  while(groupSel.options[0])
    groupSel.remove(0);
  matchShow.style.display = "none";
  showMatches();
  groupShow.innerHTML = "Select Group";
  groupShow.removeEventListener("click",showAll,true);
  groupShow.addEventListener("click",hideAll,true);
}
function hideMatches(){
  var matchTables = document.getElementsByClassName("matchTable");
  var matches = document.getElementsByClassName("matchDiv");
  for(i = 0; i < matchTables.length; ++i){
    matchTables[i].removeEventListener("mouseover",matchMouseOver);
    matchTables[i].addEventListener("mouseover",matchMouseOver);
    matchTables[i].addEventListener("click",matchTableClick);
  }
  for(i = 0; i < matches.length; ++i){
    matches[i].style.display = "none";
  }
  matchShow.innerHTML = "All Matches";
  matchShow.removeEventListener("click",hideMatches,true);
  matchShow.addEventListener("click",showMatches,true);
}
function showMatches(){
  var matchTables = document.getElementsByClassName("matchTable");
  var matches = document.getElementsByClassName("matchDiv");
  for(i = 0; i < matchTables.length; ++i){
    matchTables[i].removeEventListener("click",matchTableClick);
  }
  for(i = 0; i < matches.length; ++i){
    matches[i].style.display = "";
  }
  selectedMatch = null;
  matchShow.innerHTML = "Select Match";
  matchShow.removeEventListener("click",showMatches,true);
  matchShow.addEventListener("click",hideMatches,true);
}
function teamMouseOver (event){
  rowMouseOver(event,true);
}
function matchMouseOver (event){
  rowMouseOver(event,false);
}
function rowMouseOver(event,isTeam){
  var grouprows = [], matchrows = [], allRows = [];
  var element = event.target;
  while(element.tagName != "TABLE" && element.tagName != "TR")
    element = element.parentNode;
  if(element.tagName == "TR" && element.rowIndex > 0 && !element.contains(event.relatedTarget) && element.classList[0]){
    if(isTeam){
      grouprows = [element];
      matchrows = document.querySelectorAll("div.groupDiv table.matchTable tr."+element.classList[0]);
    }else{
      matchrows = [element];
      grouprows[0] = document.querySelector("div.groupDiv table.groupTable tr."+element.classList[0]);
      grouprows[1] = document.querySelector("div.groupDiv table.groupTable tr."+element.classList[1]);
    }
    for(var i = 0;grouprows && i < grouprows.length; ++i){
      allRows.push(grouprows[i]);
      for(var j = 0; j<grouprows[i].cells.length;++j){
        grouprows[i].cells[j].dataset.Background = grouprows[i].cells[j].style.background;
        grouprows[i].cells[j].style.background = rowHoverBG;
      }
    }
    for(var i = 0;matchrows && i < matchrows.length; ++i){
      allRows.push(matchrows[i]);
      for(var j = 0; j<matchrows[i].cells.length;++j){
        matchrows[i].cells[j].dataset.Background = matchrows[i].cells[j].style.background;
        matchrows[i].cells[j].style.background = rowHoverBG;
      }
    }
  }else//end if homeRows
    return;
  element.addEventListener("mouseout",(function(){
    return function (event){
      if(element.contains(event.relatedTarget))
        return;
      rowMouseOut(allRows);
      element.removeEventListener("mouseout",arguments.callee,false);
    };
  })(),false);
}
function rowMouseOut (rows){
  for(var row of rows){
    for(var i = 0; i < row.cells.length; ++i){
      row.cells[i].style.background = row.cells[i].dataset.Background;
      delete row.cells[i].dataset.Background;
    }
  }
}
function matchTableClick(event){
  if(event.target.tagName == "TR" && event.target.rowIndex > 0){
    var match = document.getElementById(event.target.dataset.matchid);
    if(match){
      if(selectedMatch)
        selectedMatch.style.display = "none";
      selectedMatch = match;
      match.style.display = "";
    }
  }
}
function selchange(){
  if(selectedGroup)
    selectedGroup.style.display = "none";
  if(selectedMatch){
    selectedMatch.style.display = "none";
    selectedMatch = null;
  }
  selectedGroup = document.getElementById(this.value);
  selectedGroup.style.display = "";
}
</script>
<div style="width:100%; background:#CCCCCC; max-width:800px; padding:2px; display:none;" data-rowHoverColor="#DDDDDD" id="groupBrowseControls">
<div style="display:inline-block; padding-right:20px;"><select id="groupSel"></select></div>
<div style="display:inline-block; padding-right:20px;" ><button id="matchShow">All Matches</button></div>
<div style="display:inline-block;" ><button id="groupShow">All Groups</button></div></div>