GDevelop supports JavaScript to create your game or extend the game engine.
GDevelop supports adding JavaScript code blocks at any point in the events of your game. It's a good way to implement a complex algorithm or reuse functions from open-source libraries. Events and code blocks can seamlessly be mixed together - so you can implement parts or even the totality of your game with JavaScript!
The JavaScript editor is based on the super powerful Monaco Editor, extracted from Visual Studio Code. Intellisense autocompletions are provided and the editor supports advanced features like multi-selection for faster coding.
Learn more about using JavaScript.
GDevelop is modular and can be extended to suit your needs. In particular, all features available to games (objects, behaviors, events) are based on the extension system. You can quickly create new extensions for your game or contribute to existing ones as GDevelop is open-source.
Learn how to write JavaScript powered extensions and read the game engine reference documentation.
Finally, note that in most cases you don't even need to quit GDevelop to write an extension in JavaScript, as most extensions can be built in the editor, directly in your game project.