代码如下：
<script> function call_me(max_length) { if((document.form1.mybox.value == null ) || (document.form1.mybox.value == "" )) document.form1.mybox.size = size; if((document.form1.mybox.value.length >= size)&&(document.form1.mybox.value.length <= max_length)) document.form1.mybox.size = document.form1.mybox.value.length + 1; else document.form1.mybox.size = size; } </script> <form name="form1"> <div align="center">试试撑开这个文本框: <input type="text" style="font-family: Terminal" name="mybox" maxlength="30" size="10" onFocus="setInterval('call_me(document.form1.mybox.maxLength)', 1)"> </div> </form> <script> var size = document.form1.mybox.size; </script>