function TableCss(options){
  //如果没参数,就退出
  if(arguments.length < 1 || !document.getElementById(options.tableName) ) { return ;}
  //参数及默认参数
  var options = {
    tableName : options.tableName,
    evenClass : options.evenClass || "tr_even",
    oddClass : options.oddClass || "tr_odd",
    clickClass : options.clickClass || "tr_click",
    hoverClass: options.hoverClass || "tr_hover"
    }
  //根据ID找到表格元素
  var tableName = document.getElementById(options.tableName);
  var tr = tableName.getElementsByTagName("tr");
  //对TR元素循环设置
  for(var i=0, len=tr.length; i<len; i++){
    //用了闭包
    (function(k){
      //设置奇偶行样式
      tr[k].className = (k%2==0)? options.oddClass : options.evenClass;
      //点击样式
      tr[k].onclick = function(){
        if (tr[k].className == options.clickClass){
          tr[k].className = (k%2==0)? options.oddClass : options.evenClass;
        }
        else {
          tr[k].className = options.clickClass;
        }
      }
      //鼠标HOVER样式,如果已经是点击样式,则不变化
      tr[k].onmouseover = function(){
        if(tr[k].className == options.clickClass ){ return false;}
        else { tr[k].className = options.hoverClass;}
      }
      tr[k].onmouseout = function(){
        if(tr[k].className == options.clickClass){ return false;}
        else {
         tr[k].className = (k%2==0)? options.oddClass : options.evenClass;
        }
      }
     })(i)
  }
}
//调用
TableCss({tableName:"tb1"});

<style>
<!--
#tb1,
#tb1 td{ border:1px solid #000;border-collapse:collapse}
.tr_even { background:#CCC;}
.tr_odd { background:#9FF;}
.tr_hover { background:#FF6;}
.tr_click { background:#00F;}
-->
</style>
<table id="tb1" cellpadding="1" cellspacing="1">
  <tr>
    <td>123</td>
    <td>456</td>
    <td>123</td>
    <td>456</td>
    <td>123</td>
    <td>456</td>
  </tr>
  <tr>
    <td>123</td>
    <td>456</td>
    <td>123</td>
    <td>456</td>
    <td>123</td>
    <td>456</td>
  </tr>
  <tr>
    <td>123</td>
    <td>456</td>
    <td>123</td>
    <td>456</td>
    <td>123</td>
    <td>456</td>
  </tr>
  <tr>
    <td>123</td>
    <td>456</td>
    <td>123</td>
    <td>456</td>
    <td>123</td>
    <td>456</td>
  </tr>
</table>