Updating a textbox before the form is submitted

Hi all,

 I am writing a control extender for textboxes. When the user submits the form (may be partial or a full post back) I want to check the textbox text property (value property in JavaScript) and update it.

I added a handler to Application object's unload event using Sys.Application.add_unload() method. My handler did fire when the page got unloaded, but it happens after the data is submitted, so any update I do on the textbox is irrelevant because the data was submitted already.

Is there any other method I can use in order to achieve the ability to evaluate the textbox's text and do something with it before the data is sent?

I thought about attaching to the form's onSubmit event, but I am pretty sure it will not work when validators are in the page. Their validation method stops the onSubmit handlers chain, right?

Thank you for your time,


To Infinity and Beyond!
6/21/2007 10:26:56 PM
asp.net.ajax-ui 9760 articles. 0 followers. Follow

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 Hi David,

       I read your problem, but still not perfectly clear about what you are trying to do.  [ When the user submits the form (may be partial or a full post back) I want to check the textbox text property (value property in JavaScript) and update it.], I want to be clear on this line.

From whatever I've understood..... 

 Do you want to check the the textbox's value and and do some manipulation before the data is submitted? You can call a javascript on  "OnTextChanged" event and check it at the time the user is entering the text.


And since you have posted it here in AJAX forum, how are you using AJAX here?

can you give more detail of your problem.



Mehul Mistry

If you feel your question is answered then please click "Mark As Answer" to the post that answered it. Thanks :-)
6/22/2007 6:21:36 AM


I am posting this message here be cause the forum's description states that it relates among other stuff to client API. My post is about control extenders which rely on Sys.UI.Behavior, which is a part of this API, isn't it? :-)

You understood exactly what I want to do. I want to manipulate (if required) the textbox's text (in javascript) right before the form's submission, so the new value it has will be reflected in server side events in this postback.

I don't want to use onChange event because this means the manipulation will take place when the control loses focus. I want to manipulate it right before the forms submits.

Thank you for your reply,


To Infinity and Beyond!
6/22/2007 6:57:40 AM

HI David,

    Are you having any button in your form which is submitting your form. If so, you can try the following....

1. Add your javascript function you want to manipulate in the aspx file.

2. In the code behind, add the javascript function call to the button on click event as Button2.Attributes.Add("onClick", "myJavaScriptFunction();")   in the page load event.Alternative you can do the same thing by adding the javascript function name to the Button's OnClientClick event. In this the javascript function is called first and you can manipulate the content of the textbox and in the code behind you will be able to get the modified value of the textbox.


eg: <script  type="text/javascript">

     function myJavaScriptFunction() {
                    document.getElementById("TextBox1").value = "from javascript" ;


For your button you can do <asp:Button ID="Button2" runat="server" Text="Button" OnClientClick="myJavaScriptFunction() "  />   or in the page load in the code behind you add Button2.Attributes.Add("onClick", "test();").

Hope this might help. Also if any other control (apart from button) in your form is causing a postback the to that control also you do the above thing and it should solve the prob.



Mehul Mistry

If you feel your question is answered then please click "Mark As Answer" to the post that answered it. Thanks :-)
6/22/2007 8:25:32 AM

 Hi Mehul,

First thanks for the thorough reply!

I am not sure this is a good solution for me, the hook should come from the extender and not from the button. This for several reasons:

  1. This is an extender, the whole idea is that you don't need to edit anything in the page. Adding the extender and setting only the extender's properties is the right method.
  2. Since an extender is a pluggable component no one can "promise" me that everytime this extender is used there will be a button in the page as well.

There is another important issue - validators. They are hooked to the Form's OnSubmit event. So if I hook my extender to the same event it may not be fired (the validation handler has a "return" in the end, so the handlers chain is interrupted).

Do you happen to know if there is a way to hook to an event like OnBeforeValidation or something like this?

I was sure this is a simple challenge,  now I am not that sure of it...

Thanks again,

To Infinity and Beyond!
6/22/2007 9:43:55 AM

Hi All,

Problem solved.

I don't know how I missed it, but the solution is pretty simple (as I thought it should be...):

this._form = $get('form1');
if (this._form != null) {
            this._submitHandler = Function.createDelegate(this, this._onSubmit);
            $addHandler(this._form, 'submit', this._submitHandler);

in this._onSubmit I evaluate the textbox value and manipulate it if required. I checked it with validators as well and it is working just fine.

I want to thank Damian Meher for opening my eyes!

Good Day,

To Infinity and Beyond!
6/22/2007 7:30:40 PM

Thanks davidtravis Smile

Chetan Sarode
Software Engineer,
Approva Systems Pvt Ltd,
Pune, India.
6/23/2007 3:59:52 AM

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