script type="text/javascript">
    $(function () { 
      $("#txtEmail").blur(function () {
        $.ajax({
          type: "post",
          url: "reg.ashx?email=" + $.trim($("#txtEmail").val()) + "d=" + (+new Date()),
          success: function (data) {
            var vCount = parseInt(data);
            if (vCount == 0) {
              alert("郵箱可以使用");
            }
            else {
              alert("郵箱已經被占用");
            }
          }
        });
      });
      $("#checkpwd").blur(function () {
        return CheckPwd();
      });
    });
    function CheckPwd()
    {
      var bCheck = true;
      if ($.trim($("#pwd").val()) != $.trim($("#checkpwd").val()))
      {
        alert("兩次密碼輸入不一致");
        bCheck = false;
      }
      return bCheck;
    }
  /script>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
namespace WebT1.Ti.html2
{
  /// summary>
  /// reg 的摘要說明
  /// /summary>
  public class reg : IHttpHandler
  {
    public void ProcessRequest(HttpContext context)
    {
      if (context.Request["email"] != null)
      {
        string strEmail = context.Request["email"];
        ListUserModel> lstUser = DataService.GetUserList();
        var v = lstUser.Where(p => p.Email == strEmail);
        int iCount = 0;
        if (v.Count() > 0)
        {
          iCount = 1;
        }
        context.Response.ContentType = "text/plain";
        context.Response.Write(iCount.ToString());
      }
    }
    public bool IsReusable
    {
      get
      {
        return false;
      }
    }
  }
  public class DataService
  {
    /// summary>
    /// 模擬已注冊用戶數據
    /// /summary>
    public static ListUserModel> GetUserList()
    {
      var list = new ListUserModel>();
      list.Add(new UserModel() { Email = "t1@demo.com" });
      list.Add(new UserModel() { Email = "t2@demo.com" });
      list.Add(new UserModel() { Email = "t3@demo.com" });
      list.Add(new UserModel() { Email = "t4@demo.com" });
      list.Add(new UserModel() { Email = "t5@demo.com" });
      return list;
    }
  }
  public class UserModel
  {
    public string Email { get; set; }
  }
}