Want to win a PS4? Go Premium and enter to win our High-Tech Treats giveaway. Enter to Win

x
?
Solved

javascript error when trying to use getElementById: 'null' is null or not an object?

Posted on 2008-06-19
8
Medium Priority
?
668 Views
Last Modified: 2012-05-05
I thought this was pretty simple. I have an ASP:Image named img_load. I have a javascript set up to run onclick. All I want to do is set the visibility to true. Simple right? But I'm getting a 'null' is null or not an object error when trying to do anything with my javascript object.  The image is in an update panel. Does that make a difference? Is that what's causing my error?
<script type="text/javascript">
        function show_wait()
        {
            var img;
            img = document.getElementById("img_load");
            img.visible = true;   
        }
    </script>

Open in new window

0
Comment
Question by:ohmErnie
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 2
  • 2
  • 2
  • +2
8 Comments
 
LVL 33

Expert Comment

by:raterus
ID: 21823324
Look at the source of the page as the browser sees it, find the image and use the ID it has.  My guess is it's been rewritten by asp.net.

To get this "renamed" id on the server, you need to use the ClientID function of the control.  I've used this in the past to easily make the switch.

<script type="text/javascript">
        function show_wait()
        {
            var img;
            img = document.getElementById('<%= img_load.ClientID %>');
            img.visible = true;  
        }
    </script>
0
 
LVL 1

Author Comment

by:ohmErnie
ID: 21823378
Well, when I look at the source code, I don't even see my image. Is that because I set it invisible in ASP?
0
 
LVL 16

Accepted Solution

by:
burakiewicz earned 2000 total points
ID: 21823422
if you set it to visible=false in the code behind it is never output in the html,
if you add the style attribute  img.Style.Add("visibilty", "hidden");
it will be output to the page so you can access it
0
Industry Leaders: We Want Your Opinion!

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

 
LVL 14

Expert Comment

by:Ali Kayahan
ID: 21823428
<script type="text/javascript">
        function show_wait()
        {
            var img;
            img = document.getElementById("img_load");
            img.style.display = 'block';  
        }
    </script>
0
 
LVL 16

Expert Comment

by:burakiewicz
ID: 21823433
should be
("visibility", "hidden");
0
 
LVL 33

Expert Comment

by:raterus
ID: 21823442
Yeah, if you set Visible=false on the server control, it won't even be rendered.  What you need to do is set CSS to hide the image, but the HTML will remain.

The CSS attribute to use is display:none or display:block
0
 
LVL 7

Expert Comment

by:ruscomp
ID: 21823452
It may also not be shown if you are using update panels... AJAX loaded html won't show in the source...
0
 
LVL 1

Author Closing Comment

by:ohmErnie
ID: 31468838
That worked great. All I had to do was change my javascript to set the visibility back to "visible".
0

Featured Post

Important Lessons on Recovering from Petya

In their most recent webinar, Skyport Systems explores ways to isolate and protect critical databases to keep the core of your company safe from harm.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Problem Hi all,    While many today have fast Internet connection, there are many still who do not, or are connecting through devices with a slower connect, so light web pages and fast load times are still popular.    If your ASP.NET page …
This article will give core knowledge of JavaScript and will head in to your first JavaScript program. I am Durvesh Naik and I am here to deal with this series of JavaScript. I will teach you JavaScript in part wise , as its quite boring to read big…
The viewer will learn the basics of jQuery, including how to invoke it on a web page. Reference your jQuery libraries: (CODE) Include your new external js/jQuery file: (CODE) Write your first lines of code to setup your site for jQuery.: (CODE)
The viewer will learn the basics of jQuery including how to code hide show and toggles. Reference your jQuery libraries: (CODE) Include your new external js/jQuery file: (CODE) Write your first lines of code to setup your site for jQuery…
Suggested Courses

610 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question