<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>クライアントとサーバで入力値をチェックする</title>
    <script src="JScript.js" type="text/javascript"></script>
</head>
<body>
    <form id="form1" runat="server">
   
        <asp:ScriptManager ID="ScriptManager1" runat="server" />
       
        <asp:UpdatePanel ID="UpdatePanel1" runat="server">
            <ContentTemplate>
           
                <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
                <asp:Button ID="Button1" runat="server" Text="Button" OnClientClick="return entryCase();" OnClick="Button1_Click" />
                <br />
                <asp:Label ID="msg" runat="server" Text="" ForeColor="Red"></asp:Label>
               
            </ContentTemplate>
        </asp:UpdatePanel>
       
       
    </form>
</body>
</html>

// Default.asp.cs
using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;

public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e) { }

    protected void Button1_Click(object sender, EventArgs e)
    {
        double number;
        if (double.TryParse(TextBox1.Text, out number))
            msg.Text = GetName(number);
        else
            msg.Text = TextBox1.Text + " Error!";
    }

    private string GetName(double number)
    {
        return number.ToString() + " OK!";
    }
}

// JScript ファイル

function entryCase() {
   
    var str = $get("TextBox1").value;
    //数値：+/- 小数点を考慮したつもり。
    var regExp = new RegExp("^[-+]?([0-9]+\.?[0-9]|[0-9])+$");
   
    if (!str.match(regExp)) {
        $get("msg").innerText = $get("TextBox1").value + " Error!";
        return false;
    }
}