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compressing .js and .css files on push of the website

I am not even sure if something like I want is possible, so I am asking you guys to just let me know if anyone did that before. So, my goal is to when I click on "Publish" website in VS2010, to have all javascript files compressed into one, same with css and then in my layout file change the references from all different js and css files to only those two merged ones. Is that doable? Or maybe it's doable but in more manual way?
Of course the goal here is to have only two calls to external files on the website, but when I develop I need to see all files so that I can actually work with it. I guess I could do it manually before each push, but I'd rather have it done automatically using some script or something. I didn't try anything yet, and I am not looking for ready solution, I am just looking to get to know the problem better and maybe some tips.
Thanks a lot!

This is built into ASP.net 4.5. But in the mean time, you should look at the following projects
YUI Compressor
The objective of this project is to compress any Javascript and Cascading Style Sheets to an efficient level that works exactly as the original source, before it was minified.
Cassette
Cassette automatically sorts, concatenates, minifies, caches and versions all your JavaScript, CoffeeScript, CSS, LESS and HTML templates.
RequestReduce
Super Simple Auto Spriting, Minification and Bundling solution
No need to tell RequestReduce where your resources are
Your CSS and Javascript can be anywhere - even on an external host
RequestReduce finds them at runtime automatically
SquishIt
SquishIt lets you squish some JavaScript and CSS. And also some LESS and CoffeeScript.
Combres
.NET library which enables minification, compression, combination, and caching of JavaScript and CSS resources for ASP.NET and ASP.NET MVC web applications. Simply put, it helps your applications rank better with YSlow and PageSpeed.
Chirpy
Mashes, minifies, and validates your javascript, stylesheet, and dotless files. Chirpy can also auto-update T4MVC and other T4 templates.
Scott Hanselman wrote a good overview blog post about this topic a while back.

I voted up the answer that mentioned Cassette but I'll detail that particular choice a little more. Cassette is pretty configurable, but under the most common option, it allows you to reference CSS and Javascript resources through syntax like this:
Bundles.Reference("Scripts/aFolderOfScriptsThatNeedsToLoadFirst", "first");
Bundles.Reference("Scripts/aFolderOfScripts");
Bundles.Reference("Styles/aFolderOfStyles");
You would then render these in your master or layout pages like this:
#Bundles.RenderStylesheets()
#Bundles.RenderScripts("first")
#Bundles.RenderScripts()
During development, your scripts and styles will be included as individual files, and Cassette will try to help you out by detecting changes and trying to make the browser reload those files. This approach is great for debugging into libraries like knockout when they're doing something you don't expect. And, the best part, when you launch the site, you just change the web.config and Cassette will minify and bundle all your files into as few bundles as possible.
You can find more detail in their documentation (which is pretty good though sometimes lags behind development): http://getcassette.net/documentation/getting-started

Have a look at YUI compressor # codeplex.com this could be really helpful.

What I have done before is setup a post-build event, have it run a simple batch file which minimizes your source files. Then if you're in release mode (not in debug mode), you would reference the minimized source files. http://www.west-wind.com/weblog/posts/2007/Jan/19/Detecting-ASPNET-Debug-mode

I haven't heard about publish minification. I think use should choose between dynamical minification like SquishIt or compile time like YuiCompressor or AjaxMinifier.
I prefer compile time. I don't think it's very critical to have to compile time changing files. If you have huge css/js code lines you can choose this action only for release compilation and if it helps publish this files only in needed build cinfigurations.

I don't know if there is any possible way to somehow hook into the functionality from that 'Publish' button/whatever it is, but it's surely possible to have that kind of 'static build process'.
Personally I'm using Apache ANT to script exactly what you've described there. So you're developing on your uncompressed js/html/css files and when you're done, you call like ant build which then minifies, compresses, stripes and publishes your whole web application.
Example script: https://github.com/jAndreas/typeof-NaN-2.0/blob/master/build/build.xml

Break up JavaScript file into more manageable, or using different IDE

I use Dreamweaver for development, mostly PHP, html, css, javascript. Is there anyway to break up JavaScript files? or maybe a better IDE that makes it easier to work with? It just becomes quickly difficult to read and find what I'm looking for.
Thank you!

Intellij and/or Webstorm by Jetbrains has the best JS tools I have found. It has very good (as good as it gets, for JS) intellisense (autocomplete for variables and methods) as well as refactoring for variables and methods. You can cmd+click into method definitions from anywhere, as well. Unfortunately you need to pay for them, but if you are using Dreamweaver you had to pay for that. If you are only doing html/css/javascript Webstorm is the way to go.

Yes, you should break up your javascript files into relevant parts just like you break up your php files into relevant parts. The one key factor here is they should be combined and minified before being served up to the browser so the user does not have to make several network calls to your server for each .js file.
Check out Google Minify for an easy solution to that issue.
Take a look at the JQuery source to see how they divvy up their files. Now look at their combined framework, and of course their minified framework. What is actually served up to the user looks nothing like the source.

Uh, Dreamweaver?
Definitely use a different IDE. Aptana won the poll here :)

How should I start a new JavaScript project (Testing, Developing, Building)?

I've developing JavaScript since many years but have never really thought about the whole testing, developing and building stuff - but I realized it's pretty much necessary. We've just used a Subversion repository with simple release tagging (switching to git soon). As a new bigger pure JavaScript project (using jQuery) is arriving soon, I'd like to optimize the whole process.
I already did some research but never found a good starting tutorial.
It's definetly a good idea to split classes and separate code blocks into several js-files and not a big one (as Prototype or jQuery do it). These js-files must be "build" into a single file. How do I achieve that?
It's pretty much necessary to Unit-test the stuff me and my colleagues are coding. I found the js-test-driver which has an eclipse plugin that seems to be doing his job quite good. If my developer-folder contains all these src- and src-test-files, how do I integrate this in the building process?

For testing, take a look at this: https://stackoverflow.com/questions/32809/javascript-unit-testing

For merging all of your JavaScript into one file you can use something like YUI Compressor. You need to be looking for a minimizer first, compression second. A minimizer just takes the files and merges them together and gets rid of whitespace. A compressor will actually try to optimize the js for you by changing variable names and removing unnecessary code.
As for unit testing I am unsure of how you will want to do that. There are a few unit test libraries out there. A popular tool for testing is Selenium. I don't currently do unit testing so I am out of my element there..
For setting up your code you could always look at using a JavaScript framework like ExtJS or JavaScriptMVC. Those help you with setting up your code in the proper way and also helps focus your team on the proper standards and coding structure while also writing a lot of the code for you so you don't have to re-invent the wheel.
EDIT: Just a quick after thought. Even if you don't want to use a JavaScript framework, I would suggest checking them out, especially ExtJS, just to see how they organize their code and some of the tricks they do to keep it clean.

I'll answer part of your question:
These js-files must be "build" into a
single file.
This is possible only with server side language - in ASP.NET you have built in tools for that, otherwise build your own "merger" server side file and reference that file instead of the actual .js files.

These js-files must be "build" into a single file. How do I achieve that?
Definitely keep your files separate in version control, and only merge them during the build process.
The YUI compressor mentioned elsewhere is a java-based tool that will not only merge but -- of course! -- compress your files for faster download.
If you just want a simple merge of files, a simple Perl or bash-script (or other preferred scripting language) could concatenate multiple .js files into one for release -- just make sure that the build script also updates all HTML in the release to reference only the single page.

Some software for IIS/.NET similar to JAWR (consolidate and minify Javascript)

Is there any software package/library that will produce a consolidated, minified JavaScript file for a production environment, while leaving the original files/references as-is in a development environment (so developers can work independently)?
JAWR does this (and more) for a Java/Groovy environment, but I haven't seen anything like it for the Microsoft .NET/IIS7 stack. Any pointers would be helpful. Thanks!

If you're looking for a good way to automatically compress and combine css & js files here are some options:
Xpedite Not bad: has one big disadantage: you can't combine files (js/css) that are included in usercontrols with the files in your page.
Shinkansen, I don't have a lot of experience with it, but I know it has a lot of configuration options.
The ClientDependency Framework was originally written for Umbraco. Now there is a package available via NuGet for both WebForms and MVC. It works really well and this is my favorite.

We use YUICompressor to minify our Javascript (and CSS) and it works well.
However, we've had to write our own HttpHandler to decide whether to minify or not on the fly, depending on a config setting (but it could equally be on whether it was a DEBUG or RELEASE build).
In fact, we cache the file once minified (or not), so we don't have to do the same process on every request.

YUICompressor or similar in PHP?

I've been using yuicompressor.jar on my test server for on-the-fly minimisation of changed JavaScript files. Now that I have deployed the website to the public server, I noticed that the server's policies forbid the use of exec() or its equivalents, so no more java execution for me.
Is there a decent on-the-fly JS compressor implemented in PHP? The only thing resembling this that I was able to find was Minify, but it's more of a full-blown compression solution with cache and everything. I want to keep the files separate and have the minimised files follow my own naming conventions, so Minify is a bit too complex for this purpose.
The tool, like yuicompressor, should be able to take either a filename or JavaScript as input and should either write to a file or output the compressed JavaScript.
EDIT: To clarify, I'm looking for something that does not have to be used as a standalone (i.e. it can be called from a function, rather than sniffing my GET variables). If I just wanted a compressor, Minify would obviously be a good choice.
EDIT2: A lot has changed in the five years since I asked this question. Today I would strongly recommend separating the front-end workflow from the server code. There are plenty of good tools for JS development around and except for the most trivial jQuery enhancements it's a better idea to have a full workflow with automated bundling, testing and linting in place and just deploy the minified bundles rather than the raw files.

Yes there is, it's called minify.
The only thing in to worry about in the way of complexity is setting up a group, and there's really nothing to it. Edit the groupsConfig.php file if you want multiple JS/CSS in one <script> or <link> statement:
return array(
'js-common' => array('//js/jquery/jquery-1.3.2.min.js', '//js/common.js', '//js/visuals.js',
'//js/jquery/facebox.js'),
'css-common' => array('//css/main.css', '//css/layout.css','//css/facebox.css')
);
To include the above 'js-common' group, do this:
<script type="text/javascript" src="/min/g=js-common"></script>

(i know i was looking for the exact same thing not knowing how to deal directly with the jar file using php - that's how i ended up here so i'm sharing what i found)
Minify is a huge library with tons of functionalities. However the minifying part is a very tiny class : http://code.google.com/p/minify/source/browse/trunk/min/lib/Minify/YUICompressor.php
& very very easy to use :
//set the path to the jar file
Minify_YUIcompressor::$jarFile=_ROOT.'libs/java/yuicompressor.jar';
//set the path to a writable temp folder
Minify_YUIcompressor::$tempDir=_ROOT.'temp/';
//minify
$yourcssminified=Minify_YUIcompressor::minifyCss($yourcssstringnotminified,$youroptions)
same process for js, if you need more functionalities just pick from the library & read the source to see how you can make direct call from your app.
I didn't read the question well, since minify is based on using the jar files, the op can't use it anyway with his server config
Minify also include other minifying methods than yui, for example:
http://code.google.com/p/minify/source/browse/trunk/min/lib/JSMinPlus.php?r=443&spec=svn468

Try Lissa:
Lissa is a generic CSS and JavaScript loading utility. Lissa is an extension of the YUI PHP Loader aimed at solving one of the current loader limitations; combo loading. YUI PHP Loader ships with a combo loader that is capable of reducing HTTP requests and increasing performance by outputting all the YUI JavaScript and/or CSS requirements as a single request per resource type. Meaning even if you needed 8 YUI components which ultimately boil down to say 13 files you would still only make 2 HTTP requests; one for the CSS and another for the JavaScript. That's great, but what about custom non-YUI resources. YUI PHP Loader will load them, but it loads them as separate includes and thus they miss out on benefits of the combo service and the number of HTTP requests for the page increases. Lissa works around this limitation by using the YUI PHP Loader to handle the loading and sort of YUI and/or custom resource dependencies and pairs that functional with Minify.