javascript embedded inside html

Question

I have a web application that is currently split into like 40+ javascript files. When I run the application some subset of those files need to be downloaded by the browser. Obviously, given that browsers use ~6 threads to download files, this is not the optimal solution. One optimization idea that come to my mind was to embed all those javascript files (except external ones) inside the served .aspx page. So that the browser just gets one big html file and does not need to make any round trips to the server. The html page alone may contain user specific data that will be different on every request. The scripts, however, are not changing between requests. In typical use case the page (complete with scripts) has 180KB (scripts not minified) or 130KB (minified).

Now the question: does this approach have any drawbacks performance wise (network, browsers' javascript engines)? Do you know of any big applications doing something like that? Note that I am not interested in arguments about eg. maintainability as the individual scripts will still be available as separate files during development. Same question applies to css files (even though this is less of an issue in my app).

One bit of information that may be important here: the application is one big multipage form that does not require postbacks to go between the pages, validate form, submit the form, etc. However, the application in which it is embedded may have multiple such forms.

Answer 1

In general, it is a very good idea to concatenate javascript and css files together. I'm just not so sure about "your concept". My biggest concern and question here would be, can that .aspx file change potentially in any way through (dynamic) code ? That would make in impossible for the browser to cache the file, which would be a horrible scenario.

The great thing about concatenating files is, that we have one big downstream (which still is a lot faster then downloading with several single requests and HTTP overhead) and the browser can cache this file afterwards.

There are some great build-tools and scripts available, Apache ANT is one I can really suggest. You should have a look on the HTML5 Boilerplate where they make usage of ANT very frequently.