使用jQuery Ajax结果填充自定义JavaScript对象

如果这是一个重复的问题，我很抱歉，但我找不到有效的答案。

我有一个.aspx页面，它正在调用一个填充基本员工信息的Web服务。当我在自定义对象之外调用服务时，它非常有效。一旦我将ajax功能移动到自定义对象中，我就失去了作用域，无法填充对象属性。我可以看到服务通过Firebug在json中返回数据，但对象的属性没有被填充。非常感谢在这方面的任何帮助。自定义对象JavaScript如下。

/* Begin Employee JavaScript object */
//Define the Employee object
function Employee() {}
//Define the Employee object's properties on the prototype
Employee.prototype = {
    //Properties
    EmployeeNumber: '',
    FirstName: '',
    LastName: '',
    ErrorMessage: '',
    IsFound: false
}
//Define the Search function
Employee.prototype.employeeSearch = function (pEmplNo, callback) {
    $.ajax({
        context: this,
        type: "POST",
        url: "webservice URL",
        data: '{"pEmployeeNumber":"' + pEmplNo + '"}',
        contentType: "application/json; charset=utf-8",
        dataType: "json",
        success: function (msg) {
            var me = this;
            me.EmployeeNumber = msg.d.EmployeeNumber;
            me.FirstName = msg.d.FirstName;
            me.LastName = msg.d.LastName;
            me.ErrorMessage = '';
            me.IsFound = true;
            callback(me);
        },
        error: function () {
            var me = this;
            me.ErrorMessage = 'Error retrieving employee';
            me.IsFound = false;
        }
    });
}
/* End Employee JavaScript object */
function SetEmployeeFields(pEmployee) {
    $('#<%= txtEmployeeNumber.ClientID %>').val(pEmployee.EmployeeNumber);
    $('#<%= txtFirstName.ClientID %>').val(pEmployee.FirstName);
    $('#<%= txtLastName.ClientID %>').val(pEmployee.LastName);
}
function FindEmployee(emplNo) {
    $("#mdlGetEmployeeDialog").dialog('open');
    if (emplNo.length < 6) {
        while (emplNo.length < 6) {
            emplNo = "0" + emplNo;
        }
        $('#<%= txtEmployeeNumber.ClientID %>').val(emplNo);
    }
    var _employee = new Employee();
    _employee.employeeSearch(emplNo, function () {
        if (_employee.IsFound) {
            SetEmployeeFields(_employee);
            $('#<%= txtNature.ClientID %>').focus();
            $("#mdlGetEmployeeDialog").dialog('close');
        }
        else {
            $('#<%= lblMessage.ClientID %>').text('Could not find employee' + _employee.ErrorMessage);
            $('#<%= upErrors.ClientID %>').addClass("ui-state-error").css({ "padding": "4px", "margin-top": "4px" }).show();
            $("#mdlGetEmployeeDialog").dialog('close');
        }
    });
}
//Sets up the Employee Search modal and button
function SetupGetEmployeeModal() {
    $("#mdlGetEmployeeDialog").dialog({
        autoOpen: false,
        modal: true,
        width: 500
    });
    $("#btnEmployeeSearch").button({
        text: false,
        icons: {
            primary: "ui-icon-search"
        }
    }).css({
        'padding': '4px 0px 4px 0px',
        'font-size': '9px',
        'margin-left': '3px'
    });
}
$(function () {
    $('#btnEmployeeSearch').click(function (e) {
        e.preventDefault();
        var emplNo = $('#<%= txtEmployeeNumber.ClientID %>').val();
        if (emplNo !== '' && emplNo !== '######') {
            $('#<%= lblMessage.ClientID %>').text('');
            $('#<%= upErrors.ClientID %>').removeClass('ui-state-error').removeAttr('style').hide();
            FindEmployee(emplNo);
        }
        else {
            $('#<%= lblMessage.ClientID %>').text('Employee Number required');
            $('#<%= upErrors.ClientID %>').addClass("ui-state-error").css({ "padding": "4px", "margin-top": "4px" }).show();
            $("#mdlGetEmployeeDialog").dialog('close');
        }
    });
});
/* End Page Scripts */