javascript中怎么获取表格中的当前行号

<table width="100%" border="1"> 
  <tr onclick=alert(this.rowIndex)> 
    <td>&nbsp; </td> 
  </tr> 
  <tr onclick=alert(this.rowIndex)> 
    <td>&nbsp; </td> 
  </tr> 
  <tr onclick=alert(this.rowIndex)> 
    <td>&nbsp; </td> 
  </tr> 
  <tr onclick=alert(this.rowIndex)> 
    <td>&nbsp; </td> 
  </tr> 
  <tr onclick=alert(this.rowIndex)> 
    <td>&nbsp; </td> 
  </tr> 
</table>

?

既然行是this.rowIndex，我估计列号是this.collIndex