<%@ Page Language="C#" AutoEventWireup="true" CodeFile="text_area.aspx.cs" Inherits="text_area" %> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head runat="server"> <title>纯JS限制文本框字数</title> <script type="text/javascript"> window.onload = function() { document.getElementById("txtContent").onkeyup = function() { var len = this.value.length; var tmp = 10 - len; if (tmp <= 0) { this.value = this.value.substring(0, 10); document.getElementById("mes").innerHTML = "您还可以输入 0 个字符"; } else { document.getElementById("mes").innerHTML = "您还可以输入 " + tmp + " 个字符"; } } } </script> </head> <body> <form id="form1" runat="server"> <asp:TextBox ID="txtContent" TextMode="MultiLine" runat="server" Height="190px" Width="439px"></asp:TextBox> <div id="mes"> 您还可以输入 10 个字符 </div> </form> </body> </html>