javascript上下方向键控制表格行选中并高亮显示的

<style>
tr.highlight {
 background:#08246B;
 color:white;
}
</style>
<table border="1" width="70%" id="ice">
 <tr onClick="selectTR();return false;">
  <td>123</td>
  <td>234</td>
  <td>abc</td>
  <td>def</td>
 </tr>
 <tr onClick="selectTR();">
  <td>123</td>
  <td>234</td>
  <td>abc</td>
  <td>def</td>
 </tr>
 <tr onClick="selectTR();">
  <td>123</td>
  <td>234</td>
  <td>abc</td>
  <td>def</td>
 </tr>
 <tr onClick="selectTR();">
  <td>123</td>
  <td>234</td>
  <td>abc</td>
  <td>def</td>
 </tr>
 <tr onClick="selectTR();">
  <td>123</td>
  <td>234</td>
  <td>abc</td>
  <td>def</td>
 </tr>
</table>
<script language="javascript"> 
<!-- 
var currentLine = -1; 
document.onkeydown = function(e)  
{ 
  e = window.event || e; 
  switch(e.keyCode)  
  { 
    case 38: 
      currentLine--; 
      changeItem(); 
      break; 
    case 40: 
      currentLine++; 
      changeItem(); 
      break; 
    default: 
      break; 
  } 
} 
function selectTR()
{
 currentLine=window.event.srcElement.parentElement.rowIndex;
 //alert(currentLine);
 changeItem();
}
//改变选择项目 
function changeItem() 
{ 
  if(document.all) 
    var it = document.getElementById("ice").children[0]; 
  else 
    var it = document.getElementById("ice");

  for(i=0;i<it.rows.length;i++)  
  { 
    it.rows[i].className = ""; 
  } 
  if(currentLine < 0) 
    currentLine = it.rows.length - 1; 
  if(currentLine == it.rows.length) 
    currentLine = 0; 
  it.rows[currentLine].className = "highlight"; 
} 
//--> 
</script>