javascript如何实现一个table中的两个字段计算

例如:

<table width="100%" border="0" align="center" cellpadding="0" cellspacing="0" class="table">
  <tr>
  <td><table id="tb" width="100%" border="0" cellpadding="0" cellspacing="1" bgcolor="#EEEEEE">
  <tr >
   
  <td class="td_center" width="10%" nowrap>薪资项目</td>
  <td class="td_center" width="10%" nowrap>计算金额</td>
<td class="td_center" width="10%" nowrap>调整金额</td>
<td class="td_center" width="10%" nowrap>合计</td>
  </tr>
  <tr class="tr2" onMouseOut="this.style.backgroundColor='';this.style.color=''" 
  onMouseOver="this.style.backgroundColor='#E2FFFD'">
   
  <td align="center">基本工资</td>
  <td align="center">1000</td>
  <td align="center"><input type="text"></td>
  <td align="center"><input type="text" readonly></td>

  </tr>
</tabl