CoffeeScript

CoffeeScript is a little language that compiles into JavaScript. Underneath that awkward Java-esque patina, JavaScript has always had a gorgeous heart. CoffeeScript is an attempt to expose the good parts of JavaScript in a simple way.
The golden rule of CoffeeScript is: “It’s just JavaScript.” The code compiles one-to-one into the equivalent JS, and there is no interpretation at runtime. You can use any existing JavaScript library seamlessly from CoffeeScript (and vice-versa). The compiled output is readable, pretty-printed, and tends to run as fast or faster than the equivalent handwritten JavaScript.
Latest Version: 2.7.1
CoffeeScript on the topleft, compiled JavaScript output on the bottomright. The CoffeeScript is editable!
The biggest change in CoffeeScript 2 is that now the CoffeeScript compiler produces modern JavaScript syntax (ES6, or ES2015 and later). A CoffeeScript => becomes a JS =>, a CoffeeScript class becomes a JS class and so on. Major new features in CoffeeScript 2 include async functions and JSX. You can read more in the announcement.
There are very few breaking changes from CoffeeScript 1.x to 2; we hope the upgrade process is smooth for most projects.
Most modern JavaScript features that CoffeeScript supports can run natively in Node 7.6+, meaning that Node can run CoffeeScript’s output without any further processing required. Here are some notable exceptions:
This list may be incomplete, and excludes versions of Node that support newer features behind flags; please refer to node.green for full details. You can run the tests in your browser to see what your browser supports. It is your responsibility to ensure that your runtime supports the modern features you use; or that you transpile your code. When in doubt, transpile.
For compatibility with other JavaScript frameworks and tools, see Integrations.
The command-line version of coffee is available as a Node.js utility, requiring Node 6 or later. The core compiler however, does not depend on Node, and can be run in any JavaScript environment, or in the browser (see Try CoffeeScript).
To install, first make sure you have a working copy of the latest stable version of Node.js. You can then install CoffeeScript globally with npm:
This will make the coffee and cake commands available globally.
If you are using CoffeeScript in a project, you should install it locally for that project so that the version of CoffeeScript is tracked as one of your project’s dependencies. Within that project’s folder:
The coffee and cake commands will first look in the current folder to see if CoffeeScript is installed locally, and use that version if so. This allows different versions of CoffeeScript to be installed globally and locally.
If you plan to use the --transpile option (see Transpilation) you will need to also install @babel/core either globally or locally, depending on whether you are running a globally or locally installed version of CoffeeScript.
Once installed, you should have access to the coffee command, which can execute scripts, compile .coffee files into .js, and provide an interactive REPL. The coffee command takes the following options:
To use --transpile, see Transpilation.
If you’d like to use Node.js’ CommonJS to require CoffeeScript files, e.g. require './app.coffee', you must first “register” CoffeeScript as an extension:
If you want to use the compiler’s API, for example to make an app that compiles strings of CoffeeScript on the fly, you can require the full module:
The compile method has the signature compile(code, options) where code is a string of CoffeeScript code, and the optional options is an object with some or all of the following properties:
CoffeeScript 2 generates JavaScript that uses the latest, modern syntax. The runtime or browsers where you want your code to run might not support all of that syntax. In that case, we want to convert modern JavaScript into older JavaScript that will run in older versions of Node or older browsers; for example, { a } = obj into a = obj.a. This is done via transpilers like Babel, Bublé or Traceur Compiler. See Build Tools.
From the root of your project:
To make things easy, CoffeeScript has built-in support for the popular Babel transpiler. You can use it via the --transpile command-line option or the transpile Node API option. To use either, @babel/core must be installed in your project:
Or if you’re running the coffee command outside of a project folder, using a globally-installed coffeescript module, @babel/core needs to be installed globally:
By default, Babel doesn’t do anything—it doesn’t make assumptions about what you want to transpile to. You need to provide it with a configuration so that it knows what to do. One way to do this is by creating a .babelrc file in the folder containing the files you’re compiling, or in any parent folder up the path above those files. (Babel supports other ways, too.) A minimal .babelrc file would be just { "presets": ["@babel/env"] }. This implies that you have installed @babel/preset-env:
See Babel’s website to learn about presets and plugins and the multitude of options you have. Another preset you might need is @babel/plugin-transform-react-jsx if you’re using JSX with React (JSX can also be used with other frameworks).
Once you have @babel/core and @babel/preset-env (or other presets or plugins) installed, and a .babelrc file (or other equivalent) in place, you can use coffee --transpile to pipe CoffeeScript’s output through Babel using the options you’ve saved.
If you’re using CoffeeScript via the Node API, where you call CoffeeScript.compile with a string to be compiled and an options object, the transpile key of the options object should be the Babel options:
You can also transpile CoffeeScript’s output without using the transpile option, for example as part of a build chain. This lets you use transpilers other than Babel, and it gives you greater control over the process. There are many great task runners for setting up