未捕获的类型错误：无法读取 null 的属性“值”

Question

Hello I am working on an ASP.NET page where I want to view data from database using AJAX

What I have done is created the following C# method:

[System.Web.Services.WebMethod, ScriptMethod(ResponseFormat = ResponseFormat.Json, UseHttpGet = false)]
public static void ViewData(string contNumber, string BookingNo)
{
    if (contNumber != "" && BookingNo != "")
    {
        string container = contNumber;
        string booking = BookingNo;

        db.SelectData(container, booking);
        HttpContext.Current.Response.Write("IN!!"+ booking);
    }
}

I then call this method using AJAX, here the code:

<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script

        function View() {

            var container = document.getElementById("#<%=contNoTxtBox.ClientID%>").value;
            var booking = document.getElementById("#<%=bookingNoTxtBox.ClientID%>").value;

          //  var cont = container.value;
         //   var book = booking.value;

            $.ajax(
                {

                    type: "POST",
                    url: "VGMForm.aspx/ViewData",
                    data: '{contNumber: "' + $(container) + '", BookingNo: "' + $(booking) + '"}',
                    contentType: "application/json; charset=utf-8",
                    dataType: "json"

                });


        }

From my HTML page I call the function using the following code:

<input id="Button1" type="button" value="button" onclick="View()" />

However, when I click on the button, I receive the following error:

Uncaught TypeError: Cannot read property 'value' of null

I am unsure as to what is causing this error, what is the cause and how can I resolve it?

Answer 1

Some of getElementById returns null

  document.getElementById("#<%=contNoTxtBox.ClientID%>")

or

  document.getElementById("#<%=bookingNoTxtBox.ClientID%>")

Answer 2

I was able to solve it by removing the .ClientID from the script as the following:

var container = document.getElementById("contNoTxtBox").value;
 var booking = document.getElementById("bookingNoTxtBox").value;