文本框输入字数限制以及计算剩余字数

没有加htc时代码(head)

<script language="javascript">
        function checkLength(which) {
            var maxChars = 20;
            if (which.value.length > maxChars)
                which.value = which.value.substring(0,maxChars);
                var curr = maxChars - which.value.length;
                document.getElementById("chLeft").innerHTML = curr.toString();
            }
    </script>

    <div>
        <asp:TextBox ID="txtInput" runat="server" Width="200px" Height="60px" onkeydown="checkLength(this);" TextMode="MultiLine"></asp:TextBox>
        <br />
        <small>文字最大长度: 20. 还剩: <span id="chLeft">20</span>.</small>
    </div>