CoffeeScript

With PyCharm, you can use CoffeeScript that compiles into JavaScript. PyCharm recognizes *.coffee files and marks them with . You can set breakpoints directly in your CoffeeScript code and PyCharm recognizes them using source maps generated during compilation.

PyCharm helps you write CoffeeScript code by suggesting completion for keywords, labels, variables, parameters and functions. You can jump from a symbol to its declaration Ctrl+B or implementation Ctrl+Alt+B as well as find any symbol by its name Ctrl+Alt+Shift+N.

PyCharm integrates with the coffeescript compiler that translates CoffeeScript code into JavaScript. The tool also creates source maps that set correspondence between lines in your CoffeeScript code and in the generated JavaScript code so that PyCharm debugger recognizes breakpoints in your CoffeeScript code and processes them correctly.

Before you start

Make sure you have Node.js on your computer.
Make sure the CoffeeScript and File Watchers required plugins are enabled on the Settings/Preferences | Plugins page, tab Installed, see Managing plugins for details.

Compiling CoffeeScript into JavaScript

To compile your code automatically, you need to configure a CoffeeScript File Watcher which will track changes to your files and run the coffeescript compiler.

When you open a file, PyCharm checks whether an applicable File Watcher is available in the current project. If such File Watcher is configured but disabled, PyCharm displays a popup that informs you about the configured File Watcher and suggests to enable it.

If an applicable File Watcher is configured and enabled in the current project, PyCharm starts the compiler automatically upon the event specified in the New Watcher dialog.

If the Auto-save edited files to trigger the watcher checkbox is selected, the File Watcher is invoked as soon as any changes are made to the source code.
If the Auto-save edited files to trigger the watcher checkbox is cleared, the File Watcher is started upon save (File | Save All, Ctrl+S) or when you move focus from PyCharm (upon frame deactivation).

Learn more from File Watchers.

The compiler stores the generated output in a separate file. The file has the name of the source CoffeeScript file and the extension .js or .js.map depending on the compiler type. The location of the generated files is defined in the Output paths to refresh field of the New Watcher dialog. Based on this setting, PyCharm detects the compiler output. However, in the Project tool window, they are shown under the source coffee file which is now displayed as a node.

Install the CoffeeScript compiler

In the embedded Terminal (Alt+F12) , type one of the following commands:
- npm install --global coffeescript for global installation.
- npm install --save-dev coffeescript to install CoffeeScript as a development dependency.
  Learn more from the CoffeeScript official website.

Create a CoffeeScript File Watcher

Press Ctrl+Alt+S to open the IDE settings and select Tools | File Watchers.
Click or press Alt+Insert and choose the CoffeeScript predefined template from the list. Your code will be translated to JavaScript and supplied with generated source maps.
In the Program field, specify the path to the coffee.cmd file. Type the path manually or click and choose the file location in the dialog that opens.
Proceed as described in File Watchers.

Examples of customizing the behaviour of a compiler

With PyCharm, you can adjust the compiler by passing arguments to it just as if you were working in the command-line mode. Below are two examples of customizing the default output location for the CoffeeScript compiler.

Suppose, you have a project with the following folder structure:

File Watchers example of folder structure

By default, the generated files will be stored in the folder where the original file is. You can change this default location and have the generated files stored in the js folder. Moreover, you can have them stored in a flat list or arranged in the folder structure that repeats the original structure under the app node.

Store all the generated files in the output js folder

In the Arguments field, type:
--output $ProjectFileDir$\js\$FileDirRelativeToProjectRoot$\ --compile --map $FileName$
In the Output paths to refresh field, type:
$ProjectFileDir$\js\$FileDirRelativeToProjectRoot$\$FileNameWithoutExtension$.js:$ProjectFileDir$\js\$FileDirRelativeToProjectRoot$\$FileNameWithoutExtension$.map
As a result, the project tree looks as follows:

Preview compilation results without running the compiler

PyCharm can perform static analyses of your CoffeeScript code without actually running a compiler and display the predicted compilation output in the dedicated read-only viewer.

Open the desired CoffeeScript file in the editor, and right-click the editor background.
From the context menu, choose Preview Compiled CoffeeScript File. The preview is opened in the dedicated read-only viewer: the left-hand pane shows the original CoffeeScript source code and the right-hand pane shows the JavaScript code that will be generated by the compiler when it runs.

Running CoffeeScript

There are two ways to run CoffeeScript in PyCharm:

Compile the CoffeeScript code manually and then run the output JavaScript code as if it were a Node.js application.
Run the original CoffeeScript code through the Node.js run configuration and have PyCharm compile it on the fly.

Compile CoffeeScript manually and run the generated JavaScript code

Compile the CoffeeScript code into Javascript.
Start creating a Node.js run configuration with the following mandatory settings:
1. The Node.js engine to use. By default, the field shows the path to the interpreter specified on the Node.js page during Node.js configuration.
2. In the Working directory field, specify the location of the files referenced from the starting CoffeeScript file to run, for example, includes. If this file does not reference any other files, just leave the field empty. field
3. In the Path to Node App JS File field, specify the full path to the JavaScript file that was generated from the original CoffeeScript file during the compilation.
Save the configuration and click on the toolbar.
Proceed as while running a Node.js application.

Compile CoffeeScript on the fly during run

This mode requires that the register.js file, which is a part of the coffeescript package, is located inside your project. Therefore make sure you have the coffeescript package installed locally as described in Install the CoffeeScript compiler.
Open the starting CoffeeScript file in the editor or select in the Project tool window and choose Run <CoffeeScript_file_name> from the context menu. PyCharm runs the file with the automatically generated run/debug configuration.
Alternatively, select Create <CoffeeScript_file_name> from the context menu and check the following mandatory settings in the Run/Debug Configuration: Node.js dialog that opens:
1. The Node interpreter to use. Select the relevant interpreter configuration or create a new one. By default, the field shows the path to the interpreter specified on the Node.js page during Node.js configuration.
  For Linux and macOS, this setting is overridden by the Node.js from the path to the CoffeeScript compiler executable file.
2. In the Node parameters field, type --require coffeescript/register.
3. In the Working directory field, specify the working directory of the application. By default, the field shows the project root folder.
4. In the JavaScript file field, specify the full path to the CoffeeScript file to run.
Save the configuration and click on the toolbar.
Proceed as while running a Node.js application.

Debugging CoffeeScript

To debug CoffeeScript in PyCharm, you need source maps generated in addition to the JavaScript code. Source maps set correspondence between lines in your CoffeeScript code and in the generated JavaScript code, otherwise your breakpoints will not be recognised and processed correctly. JavaScript and source maps are generated by compiling the CoffeeScript code manually using the File Watcher of the type CoffeeScript. After that you can debug the output JavaScript code as if it were a Node.js application.

Debugging CoffeeScript is supported only in the local mode. This means that PyCharm itself starts the Node.js engine and the target application according to a run configuration and gets full control over the session.

For more details about debugging Node.js applications, see Running and debugging Node.js.

Debug CoffeeScript code

Set the breakpoints in the CoffeeScript code where necessary.
Compile the CoffeeScript code into Javascript using the File Watcher of the type CoffeeScript.
Start creating a Node.js run configuration with the following mandatory settings:
1. The Node.js engine to use. By default, the field shows the path to the interpreter specified on the Node.js page during Node.js configuration.
2. In the Working directory field, specify the location of the files referenced from the starting CoffeeScript file to run, for example, includes. If this file does not reference any other files, just leave the field empty.
3. In the Path to Node App JS File field, specify the full path to the JavaScript file that was generated from the original CoffeeScript file during the compilation.
Save the configuration and click on the toolbar.
Proceed as while starting the debugger together with a Node.js application on your computer.

Configuring syntax highlighting

You can configure CoffeeScript-aware syntax highlighting according to your preferences and habits.

In the Settings/Preferences dialog Ctrl+Alt+S, go to Editor | Color Scheme | CoffeeScript.
Select the color scheme, accept the highlighting settings inherited from the defaults or customize them as described in Colors and fonts.

Last modified: 27 August 2021