js实现控制textarea输入字符串的个数,鼠标按下抬起判断输入字符数

<table><tr>  <td width="150">短信内容：</td>  <td>   <textarea name="message" cols="96" rows="5" onKeyDown="textCounter(message,remLen,65);"     onKeyUp="textCounter(message,remLen,65);"></textarea>  <td></tr><tr><td></td>  <td>您还可以输入:<input name="remLen" type="text" value="65" size="5" readonly="readonly">个字符,每条短信最大允许输入<strong>65</strong>个字符</td></tr></table>

<script>   function textCounter(field, countfield, maxlimit) {      if (field.value.length > maxlimit)        field.value = field.value.substring(0, maxlimit);      else        countfield.value = maxlimit - field.value.length;   }</script>