Why is my ASP.NET page injecting this WebResource.axd Javascript file?

Question

When I view source on my ASP.NET page I get the following snippet:

<script type="text/javascript"> 
//<![CDATA[
var theForm = document.forms['form1'];
if (!theForm) {
    theForm = document.form1;
}
function __doPostBack(eventTarget, eventArgument) {
    if (!theForm.onsubmit || (theForm.onsubmit() != false)) {
        theForm.__EVENTTARGET.value = eventTarget;
        theForm.__EVENTARGUMENT.value = eventArgument;
        theForm.submit();
    }
}
//]]>
</script> 

<script src="/WebResource.axd?d=5lheyan7fritNTjDRpG8vA2&amp;t=633734967316503584" type="text/javascript"></script> 

the .aspx file looks kinda like this:

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Default.aspx.cs" Inherits="NaturalDateDemo._Default" %>

<form id="form1" runat="server" enableviewstate="False">
   Enter something to parse:<br />
   <asp:TextBox ID="TextBox1" runat="server" Width="270px"></asp:TextBox>
   <asp:Button ID="Button1" runat="server" Text="Parse" PostBackUrl="Default.aspx" CausesValidation="False" EnableViewState="False" UseSubmitBehavior="true" />
</form>

Both of the chunks of code (the literal code and the stuff in /WebResource.axd) seem to be related to doing JavaScript based post-backs and I can't think of any reason that my page would require JavaScript to do the post-backs.

• What is this doing?
• Where is it coming from?
• Can I get rid of it?
• How can I get rid of it?

The page this question is coming from

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A little Google work found this indicating that validation controls would cause this, but I don't think I have any validation controls.

Looking at the WebResource.axd file in detail shows a lot of what looks to be boiler plate function that I can't find any references to from anywhere.

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After further investigation it seem that my submit button is not be doing what I thought it was because it has some JavaScript in its onclick handler. However using FireBug I can see that the page is doing a full refresh (the HTTP response has the full page text) so I have no clue what that's about. OTOH I'm now seeing an __EVENTVALIDATION argument that shouldn't be there (because there is nothing to validate) so that might be interesting to look up.

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It seems based on the answerer below that what I'm running into is that the default (only?) way for ASP.NET to do a post-back is via JavaScript even when a basic HTML Form would do just fine. (Personally I think this is a stupid design choice on MS part; ASP.NET shouldn't introduce the JavaScript dependency until you ask it to do something that can't be done without it.)

Based on that opinion, several people have speculated that I don't know what I'm talking about. (I will grant that I confused the issue by miss using the term "post-back", thinking it only implies JS based stuff.) While I don't know the implementation details of ASP.NET, I do known how the general HTTP POST stuff works and my opinion is based on considering how I would implement the solution my self and not just based on how I would like it to work.

Answer 1

The answer is a lot simpler than any I've seen here: just remove the PostBackUrl from the Button and all JavaScript disappears like magic.

Without JavaScript, an HTML button cannot submit to another page than the page specified in <form action="...">. However, ASP.NET does provide a possibility to do this out-of-the-box if you specify a PostBackUrl on a Button. That's what the JavaScript is about: supporting a non-default post-back.

In this specific case your PostBackUrl is the same as the <form>'s action, but apparently ASP.NET does not special-case this and any non-empty string triggers this wrapper script.