rake assets:precompile for specific JS file - ruby-on-rails

Question

Could I run rake assets:precompile for specific JavaScript file?
Otherwise the full precompile lasts for 5 minutes and makes quick changes in JavaScript files very annoying.

Answer 1

If you wanted to precompile just one file, you could make a custom rake task to do so fairly easy.
namespace :assets do
desc "compile one js file"
task :compile_one_file => :environment do
dest = "#{Rails.root}/vendor/assets/javascripts/compiled/"
js_asset = "your_jsfile.js"
File.write(dest + js_asset, Uglifier.compile(Rails.application.assets.find_asset(js_asset).to_s))
end
end
then from the command line
rake assets:compile_one_file
Hope this helps, I find this useful for vendor js files that I don't change often such as jquery and jquery plugins. That way when im in development it speeds up my page loads keeping the asset pipeline from having to route all the separate requests for my vendor files. It just serves up one minified js file of all my vendor js.

Answer 2

Short: You can't.
During precompilation Rails goes through the Application.js file and merges all imports into one so just changing one file is simply not possible due to the compression that goes on in there. (It doesn't do anything to files not referenced from application.js)
Next up: You should not have to run rake assets:precompile during development when doing quick fixes. Only on deployment where (depending on your patience) it should be no problem having the task run 5 minutes.
You should be using the development environment during development where asset precompilation is not necessary because Rails will serve the assets unmerged and un-minified.
If you are running the Rails build in web-server through rails s this should be by default, but you can explicitly start the rails server using:
rails s RAILS_ENV=development
If the assets are still not correctly displayed or you see errors make sure you have config.assets.debug = true

Answer 3

#Tigraine is partially correct. Rails 3.1+ assets are intended to be fully managed by Rails and by default all assets will be compiled down to one js and one css asset.
HOWEVER...
Compiling down to a single asset relies on the use of an asset manifest (application.js and application.css) that is processed by the Sprockets gem. By default these manifests include a require_tree directive and it's that directive that includes all the files. If you remove that directive, you've got to do a bit more work to get your assets compiled.
If you want to build separate assets you can set a config option in application.rb.
config.assets.precompile += %w( additional/asset.css funky/stuff.js )
The above line would add the files additional/asset.css and funky/stuff.js to the list of files that would be produced when the assets are precompiled (Note that the '+=' is being used to extend the default list). To be as explicit as possible this means that you would have four assets precompiled: application.js, funky/stuff.js, application.css, and additional/asset.css.
That said, you might want to check out the guard-rails-assets gem. The gem is flexible in the way it supports precompiling; precompiling only changed assets is possible. I've heard some good feedback about it but not used it myself.

Answer 4

#Tigraine isn't correct.
It's possible, you just have to create folders and put the css files in them and import it to different files in the assets folder.
Like
application.css
*= require_self
*= require foundation_and_overrides
*= require reset
*= require_tree ./screen
Where Screen is a folder I've placed inside the stylesheet folder. like assets/stylesheets/screen/. I call the application.css with
<%= stylesheet_link_tag "application", media: "screen, projection" %>
Now, if you want to create a single css file for another layout you create that under assets/stylesheets
Like xxx.css
If you need multiple files for xxx you follow the same steps as above but the important part here is that you add this line to
production.rb
config.assets.precompile += %w( xxx.css )
Then inside the layout you add:
<%= stylesheet_link_tag "xxx", media: "screen, projection" %>

Answer 5

You can do this completely without Rails. This can make things run faster depending on your environment.
quick_compile.rb
require 'sprockets'
sprocket = Sprockets::Environment.new
sprocket.js_compressor = :uglifier # or read off config yml
sprocket.append_path('app/assets/javascripts') # the directory that holds you js src.
file = File.new('test_min.js','w+') # the output file path.
file.puts(sprocket.find_asset('test.js')) # the file to complie
file.close
If you just want to evalute the //= require statement, you can remove the js_compressor setting. Sprocket will concatenate the files required.