PyCharm 4.5.0 Help

Transpiling Dart to JavaScript

Most browsers that work with JavaScript code do not natively process Dart code. The only exception is Dartium. This dart-oriented version of Chromium contains a built-in Dart VM and therefore can run Dart code directly. For details, see

To be executed in any other browser, Dart code has to be translated into JavaScript. This operation is referred to as transpilation and the tools that perform it are called transpilers.

If you are using the pub tool, transpilation is performed during pub build using the built-in dart2js transpiler.

PyCharm also supports integration with the dart2js transpiler. In PyCharm, transpiler configurations are called File Watchers. For each supported transpiler, PyCharm provides a predefined File Watcher template. Predefined File Watcher templates are available at the PyCharm level. To run a transpiler against your project files, you need to create a project-specific File Watcher based on the relevant template, at least, specify the path to the transpiler to use on your machine.

On this page:

Creating a File Watcher

PyCharm provides a common procedure and user interface for creating File Watchers of all types. The only difference is in the predefined templates you choose in each case.

  1. To start creating a File Watcher, open the Settings dialog box by choosing File | Settings on the main menu, and then click File Watchers under the Tools node. The File Watchers page that opens, shows the list of File Watchers that are already configured in the project.
  2. Click the Add button new.png or press Alt+Insert and choose the Dart2JS predefined template from the pop-up list.
  3. In the Program text box, specify the path to the dart2js.bat file. Type the path manually or click the Browse button browseButton.png and choose the file location in the dialog box that opens. The default location is <Dart home>/dart-sdk/bin/dart2js.bat.
  4. Proceed as described on page Using File Watchers.

Transpiling the Dart code

When you open a Dart 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 pop-up window 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 it automatically upon the event specified in the New Watcher dialog.

  • If the Immediate file synchronization check box is selected, the File Watcher is invoked as soon as any changes are made to the source code.
  • If the Immediate file synchronization check box is cleared, the File Watcher is started upon save (File | Save All, Ctrl+S) or when you move focus from PyCharm (upon frame deactivation).

The transpiler stores the generated output in a separate file. The file has the name of the source Dart file and the extension js or depending on the transpiler type. The location of the generated files is defined in the Output paths to refresh text box of the New Watcher dialog. Based on this setting, PyCharm detects the transpiler output.

See Also

Last modified: 18 April 2015