<style>
*{margin:0 auto;padding: 0;font: 12 "宋体"}
table input{position: absolute;top:0;left:0;background: #fff;border:1px solid #000;z-index:1;width: 60px}
table{border-collapse:collapse; }
table td{position: relative;width: 60px}</style>
<table border="1">
  <tr>
    <td><input type="text" id="input"></td>
    <td>213123</td>
  </tr>
  <tr>
    <td>123123</td>
    <td>123123</td>
  </tr>
</table>
<script>
var i = document.getElementById('input'),
i_w = i.style.width;
i.onfocus=function(){
this.style.width=80
}
i.onblur=function(){
this.style.width=i_w;
}
</script>