求教！！！！！

Question

<td valign="top" height="50" width="230"> 
      <table width="100%" border="0" cellspacing="0" cellpadding="0">
        <tr valign="top"> 
          <td width="20%"> 
            <input type=button value="清屏" style="color: #000000; background-color: #f3f3f3; border-style: solid; border-width: 1" onMouseOver ="this.style.backgroundColor='#FFC864'" onMouseOut ="this.style.backgroundColor='#f3f3f3'" style="width=40;font-size:9pt" onClick="javascript:showmain()" name="button">
          </td>
  <script>
  function showmain()
  {
  alert("你的清屏程序放到这儿呵!");
  }
  </script>

Answer 1

alert("你的清屏程序放到这儿呵!");
求教清屏程序