asp.net server control - avoid adding multiple javascript - asp.net

Question

I created an asp.net Server control that derives from a LinkButton, and renders a small javascript function to the page.
I want to use this control many times on the page, but just want the javascript to be rendered once on the page. On the other hand, I rather not manually add it in a js file, because i don't want to have a chance of forgetting to add the js file in the future.
What will be the best way to go about doing this ?

Answer 1

Preventing duplication in client scripts
Use a registration method such as Page.ClientScript.RegisterClientScriptBlock(..). There are a couple of overloads but they all work in a similar fashion. It's smart enough to render the script only once no matter from how many control instances it's issued.
Microsoft remarks in the MSDN documentation:
A client script is uniquely identified
by its key and its type. Scripts with
the same key and type are considered
duplicates. Only one script with a
given type and key pair can be
registered with the page. Attempting
to register a script that is already
registered does not create a duplicate
of the script.
The MSDN docs also contain sample code such as this:
// Check to see if the client script is already registered.
if (!cs.IsClientScriptBlockRegistered(cstype, csname2))
{
StringBuilder cstext2 = new StringBuilder();
cstext2.Append("<script type=text/javascript> function DoClick() {");
cstext2.Append("Form1.Message.value='Text from client script.'} </");
cstext2.Append("script>");
cs.RegisterClientScriptBlock(cstype, csname2, cstext2.ToString(), false);
}
Other similar registration methods
Different methods can be used to register your client script in different ways - see each of the ClientScriptManager.RegisterClientScript*(..) methods in MSDN for more detail about each. They're all built to prevent duplication in the rendered page.
This gives you the freedom to output scripts at the control level without worrying or having to track or count scripts.
Edit:
The ClientScriptManager instance is accessed through the Page.ClientScript property.

Answer 2

You can use the Page.RegisterClientScriptBlock method.
Here is an example from the MSDN:
if (!this.IsClientScriptBlockRegistered("clientScript"))
{
// Form the script that is to be registered at client side.
String scriptString = "<script language=\"JavaScript\"> function DoClick() {";
scriptString += "myForm.show.value='Welcome to Microsoft .NET'}<";
scriptString += "/";
scriptString += "script>";
this.RegisterClientScriptBlock("clientScript", scriptString);
}
HTH

Answer 3

Any way to reference a script on a CDN and not have it duplicated multiple times? Or can I just not worry about it since it's just a pointer anyway and the browser is (?) smart enough not to load the same library twice?
In other words, suppose I want the following code inserted from a server control:
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.4.4/jquery.min.js"></script>
If I use a RegisterClientScriptBlock I can use the IsClientScriptBlockRegistered method to not have the server control load it multiple times. But, the preceding code is likely to have been put on the page anyway by either another (different) server control or by the developer who wants to use jQuery for something outside of the server control.
How do I get the server control to not load the script if the developer already loaded it?