decaffeinate 
Goodbye CoffeeScript, hello JavaScript!
JavaScript is the future, in part thanks to CoffeeScript. Now that it has served
its purpose, it's time to move on. Convert your CoffeeScript source to modern
JavaScript with decaffeinate.
Installation and usage
# via yarn
$ yarn global add decaffeinate
# via npm
$ npm install -g decaffeinate
$ decaffeinate input.coffee
input.coffee → input.js
# convert all files in directory and subdirectories
$ decaffeinate .
input.coffee → input.js
subfolder/input.coffee → subfolder/input.js
Alternatively, paste code into the online repl to immediately see the output.
For real-world use cases, you'll likely want to spend some time understanding
the different options and nuances of the decaffeinate tool. You'll also likely
want to run decaffeinate using the bulk-decaffeinate wrapper tool, or write
your own wrapper script. See the Conversion Guide for more
information and advice on running decaffeinate on real-world code, and see
Cleanup suggestions after running decaffeinate for advice on
cleaning up the converted JavaScript code and other things to keep in mind.
Questions and support
Feel free to join the gitter chat room
to ask questions, or you can file an issue on the issues page:
Status
Complete. The project is stable enough for production use, and has been used
to convert hundreds of thousands (probably millions) of lines of production
code. The conversion process has been extensively tested and there are few or no
known correctness bugs, although no guarantees are made.
Here are some popular open source CoffeeScript projects and their current status
when run through decaffeinate. Each project has a decaffeinate-specific fork
that is re-created from the original repo once per day.
| Project | Lines of CoffeeScript | Conversion status | Test status |
|---|---|---|---|
| chroma.js | 3.3K |  |
 |
| hubot [1] | 3.7K |  |
 |
| autoprefixer [1] | 4.8K |  |
 |
| coffeelint | 8.8K |  |
 |
| vimium [2] | 11K |  |
 |
| coffeescript [2] | 17K |  |
 |
| coffeescript2 [2] | 17K |  |
 |
| atom [1] | 51K |  |
 |
| atom-org | 170K |  |
 |
| codecombat | 230K |  |
 |
Project builder status: 
Notes:
- Hubot and Autoprefixer have fully moved to
JavaScript using decaffeinate. This build runs on the last commit before the
switch to JS. Atom has mostly moved to JavaScript using decaffeinate, so this
build runs on an earlier revision that was primarily CoffeeScript. - Some CoffeeScript tests are disabled because
they are difficult to fix and test situations that do not seem to come up in
real-world code. The Vimium test suite has also been modified slightly to
work around a correctness issue. See
How decaffeinate approaches correctness for full details.
To contribute to this list, send a pull request to the decaffeinate-examples
project.
In addition, decaffeinate has been used on private codebases within various
companies, such as Square, Benchling, Bugsnag, and DataFox.
Some blog posts on using decaffeinate:
- From 200K lines of CoffeeScript to zero: making decaffeinate super-stable
- Converting a large React Codebase from Coffeescript to ES6
- Decaffeinating a Large CoffeeScript Codebase Without Losing Sleep
- The Great CoffeeScript to Typescript Migration of 2017
If you run into crashes or correctness issues, or you have suggestions on how
decaffeinate could be improved, feel free to file an issue on the issues page.
Goals
- Fully automated conversion of the CoffeeScript language to modern JavaScript.
- Preserve whitespace, formatting, and comments as much as possible to allow
a full one-time conversion of your CoffeeScript source code. - Focus on correctness as the first priority, with some options to generate
nicer code at the expense of 100% correctness. - Provide helpful error messages when it encounters an unsupported language
construct.
Common options
--use-cs2: Treat the input as CoffeeScript 2 code. CoffeeScript 2 has some
small breaking changes and differences in behavior compared with CS1, so
decaffeinate assumes CS1 by default and allows CS2 via this flag.--use-js-modules: Convertrequireandmodule.exportstoimportand
export. Note that this may result in incorrect import statements because
decaffeinate does not know the export style used by the other file. To
generate correct imports, use bulk-decaffeinate and
enable theuseJSModulesoption.
Other options
--modernize-js: Treat the input as JavaScript and only run the
JavaScript-to-JavaScript transforms, modifying the file(s) in-place.--literate: Treat the input file as Literate CoffeeScript.--disable-suggestion-comment: Do not include a comment with followup
suggestions at the top of the output file.--no-array-includes: Do not useArray.prototype.includesin generated
code.--safe-import-function-identifiers: Comma-separated list of function names
that may safely be in theimport/requiresection of the file. All other
function calls will disqualify laterrequires from being converted to
imports.--prefer-let: Useletinstead ofconstfor most variables in output
code.--loose: Enable all--loose...options.--loose-default-params: Convert CS default params to JS default params.--loose-for-expressions: Do not wrap expression loop targets inArray.from.--loose-for-of: Do not wrap JSfor...ofloop targets inArray.from.--loose-includes: Do not wrap inArray.fromwhen convertingintoincludes.--loose-comparison-negation: Allow unsafe simplifications like!(a > b)toa <= b.--loose-js-modules: Allow named exports when converting to JS modules.--disallow-invalid-constructors: Give an error when constructors usethis
beforesuperor omit thesupercall in a subclass.--optional-chaining: Target JavaScript optional chaining. Note the semantics may not match exactly.--nullish-coalescing: Target JavaScript nullish coalescing. Note the semantics may not match exactly.--logical-assignment: Use the ES2021 logical
assignment operators
&&=,||=, and??=.
For more usage details, see the output of decaffeinate --help.