Insanely simple JSON templates
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jason - insanely simple JSON templates StillMaintained Status Build Status


There's no easy way to create JSON templates in Ruby.


Use Erubis to make the simplest thing that could possibly work.


gem install jason


You write jason templates in a fashion similar to regular old JSON with a notable exception: trailing commas in arrays and objects are automatically removed. This allows you to easily create JSON templates using iterators.

Jason.render('{ "foo": "bar" }') # => '{"foo":"bar"}'

  "test": [
    <% if true %>
    <% end %>
    "bar", <%# Notice how this trailing comma is perfectly valid. %>
) # => '{"test":["foo","bar"]}'

Jason also redefines the <%= expr %> Erubis delimiter so that it converts the expression to a JSON value by calling #to_json on the expression. If you'd like to use regular interpolation, use the <%== expr %> delimiter instead.

Jason.render('<%= 'test' %>') # => '"test"'
Jason.render('"<%== 'test' %>"') # => '"test"'

You can configure the output format of the JSON:

Jason.output_format = :compact # This is the default.
Jason.output_format = :pretty

:compact will remove any unnecessary whitespace in the JSON while :pretty will indent the result JSON so that it looks, well, pretty.

You can add output listeners to jason so that you can run arbitrary code upon the generated JSON. For example, if you'd like to log all of the JSON responses in Rails:

Jason.output_listeners << lambda do |hash|"[Jason] Generated output:\n#{JSON.pretty_generate(hash)}")

Usage with Rails

Name your view template with the extension jason. Everything else is the same.

# in view_name.jason
  "foo": "bar",
  "baz": [
    <% unless @we_started_the_fire %>
    <% end %>

# Renders: {"foo":"bar","baz":["quz","quuz"]}

Note on Patches/Pull Requests

  • Fork the project.
  • Make your feature addition or bug fix.
  • Add tests for it. This is important so I don't break it in a future version unintentionally.
  • Commit, but do not mess with the Rakefile. If you want to have your own version, that is fine but bump the version in a commit by itself in another branch so I can ignore it when I pull.
  • Send me a pull request. Bonus points for git flow feature branches.



Jason is licensed under the MIT License. See LICENSE for details.