source_map gem provides an API for parsing, and an API for generating source maps in ruby.
#line functionality. They allow you to
as though you had done neither of these things.
This gem helps you create or parse those mapping files according to the SourceMaps version 3 spec.
gem install source_map
Generating a source map
require 'source_map' file = File.open("public/combined.js", "w") map = SourceMap.new(:generated_output => file, :file => "combined.js", :source_root => "http://localhost:3000/") Dir["js/*"].each do |filename| map.add_generated File.read(filename), :source => filename.sub('public/', '') end map.save("public/combined.js.map")
This snippet will create two files for you.
combined.js which contains all your
combined.js.map which explains which bits of the file
came from where.
(Using the :generated_output feature to automatically write the combined.js file is totally optional if you don't need that feature).
If you want more flexibility, there's an alternative API that requires you to do a bit more manual work:
require 'source_map' map = SourceMap.new(:file => 'combined.js', :source_root => 'http://localhost:3000/') my_crazy_process.each_fragment do |x| map.add_mapping( :generated_line => x.generated_line, :generated_col => 0, :source_line => x.source_line, :source_col => 0 :source => "foo.js" ) end
If you use this API, you'll probably need to read the Spec.
Using a source map
You'll need Chrome version 19 or greater. Go to the developer console, and click on the settings cog; and then click "Enable source maps".
Now, ensure that when you load
combined.js, you also need to send an extra HTTP header:
Finally ensure that eah of the source files can be reached by appending the value you
:source, to the value you provided for
NOTE: in theory you can (instead of using the
X-SourceMap header) add a comment to the
end of your generated file (
combined.js) which looks like:
however I haven't had much luck with this.
NOTE2: In theory you could use the Closure Inspector Firefox extension instead of Chrome 19, but I couldn't get it to work either (even when I tried in Firefox 3.6 which is the most recent version it supports).
Sorry this is a bit rubbish :(.
An API to look up the position in the original source from a given position in the generated file.
I'd like to write a tool that given two source maps, composes them. Once that is done, then we could pipe
combined.jsthrough a minifier which generates a
combined.js.min.map. And then we could combine
combined.js.min.mapso that we can use our concatenated and minified code with the debugger with impunity. (The only such minifier that exists at the moment is the closure compier, maybe that will change...)
Supporting the index-file mode of SourceMaps (an alternative to the previous suggestion in some circumstances)
This stuff is all available under the MIT license, bug-reports and feature suggestions welcome.
This stuff is quite new so there's not exactly a lot of information about it: