asp.net - Scriptmanager remove javascript

Question

The ASP.NET ScriptManager control automatically inserts all kinds of inline javascript like PageRequest initialize. Is it possible to remove or move this to an external js file?

Also, the scriptmanager always adds __DoPostback even when not used on the page, how can this be avoided or also moved to an external file?

Answer 1

First of all the "__DoPostBack" is inserted by controls that can cause a postback such as the DropDownList with the AutoPostBack property set to true. Since the ScriptManager basically intercepts the traditional postbacks, I believe that's the reason for it to insert the function.

-- The following is just me thinking... :)

Now, about moving everything to an external file. It's not easy, but it "could" be possible. The problem is that ASP.NET is generating the scripts at runtime, so you cannot do anything about it statically. What you need to consider is why you would want to do this in the first place. The fact is that much of the generated script is dynamic, which makes it rather hard to cache. But, if you really need to, you should have a look at both HttpHandlers and HttpModules.

Basically you need to somehow extract every script tag (without the src-attribute set). This could be done in a HttpModule on the BeginRequest event of the HttpContext. Now you need to extract all the necessary pieces of information and replace it with a reference to a specific HttpHandler that can service as the replacement. But to make any difference at all, it is necessary for you to do some sort of caching of the existing script. You could probably use the ASP.NET Cache for that. The tricky part would be to compare an existing cache entry with the new and determine whether or not to get the cached version (pointing the HttpHandler to an existing entry) or to generate a new entry. If you have a lot of scripts, it's most likely to be a rather expensive operation. Furthermore you need to determine whether the client can cache on it's own (e-tags etc. could come in handy). What's important is for the client to avoid downloading the same unnecessary scripts each time (I believe that's your ultimate goal?).

So to recap:

• Build a HttpModule to take care of the page rewriting and putting the extracted script into some sort of cache (eg. ASP.NET Cache).
• Build a HttpHandler to point to for the extracted script (it should stream the contents from the cache). The handler should be put in place of the extracted inline scripts.
• Create some sort of algorithm for determining cache invalidity. I don't know from the top of my head what kind of script that could change between requests.

Btw. script externalization is tricky at most, so you need to be careful not to introduce bugs that are impossible to fix ;)

Not an extact solution, but I have tried doing this myself before without any luck... mostly because of too litle time. When you are payed to do a task, this kind of optimization can't be justified... :(