ASP.NET __doPostBack rendered after beginning or near end of form tag

Question

I'm trying to manually call the ASP.NET (3.5) javascript postback function __doPostBack from my javascript code. The problem is that the postback script block, that is normally rendered right after the beginning of the <form> tag (and the hidden fields), is occasionally rendered near the closing </form> tag.

Is there any way to force it to be rendered near the beginning of the form tag? Also, how does ASP.NET decide when/where to render the postback client script block?

Edit > Additional Info: The javascript code resides inside a user control that references the __doPostBack function. The control itself does not contain any 'postback controls' that would call that function. (When I mention 'postback controls', I mean ASP.net controls that call the __doPostBack function and not the asp.net ImageButton and Button controls)

Based on what I've observed and @Brian's comment on the dependency of the postback script on the availability of 'postback controls' on the page, I've found that when the page contains controls that cause postback, the __doPostBack script block is rendered after the opening <form> tag and when there are none, it renders them near the closing </form> tag (or according to this it's not even supposed to be rendered). Now it would make sense for ASP.NET not to render the postback script if there are no controls that require it, but the apparent position of the script near the closing tag is the one that still eludes me. I haven't been able to find any documentation that suggests this behavior. All I've been able to find was this.

Having said that, I've found a couple ways around this issue:

1. Add a 'postback control' and set its visibility to hidden via css (not the Visible property). eg. <asp:LinkButton ID="RequirePostBackScriptLink" runat="server" style="display:none;" /> (this is what I'm using)
2. Add the control to the Page.RegisterRequiresPostBack and implement the IPostBackDataHandler interface.

Finally, as @Jonathan_Bates mentioned in his post, the proper thing to do is to wrap the reference to __doPostBack inside a function that is an event handler to load (or ready if you're using jquery). That way, there wouldn't be a need to depend on the actual placement of the __doPostBack script.

It'd be great if anyone can provide more info on this, aforementioned, behavior.

Answer 1

Hey,

Some of it is controlled by the controls that render, whereas the page injects the client script blocks and startup scripts at a pre-defined point...

I assume this is for a control or something? This isn't for a standard block?

Answer 2

I am guessing that where it renders is important to you so that your scripts render after it and can invoke it (which let me say up front, is a bad idea to begin with).

You just need to make sure that whatever script you are using to call __doPostBack calls it after its been read into the browser. If you use a library like jQuery and its $(document).ready() convention, you can be sure that your code won't execute until all other code is loaded, and therefor your code would be able to call __doPostBack.