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HugoJS – Online Hugo Interpreter

HugoJS is an online interpreter for Hugo games.

The interpreter is running at

If you want to host the interpreter on your own web site, see Hosting your own interpreter instance.

For more documentation, see the wiki pages.

Development Environment


The build scripts are made for a Unix environment (Linux/MacOS). To use them you need npm or Yarn. npm comes with a standard Node.js installation. npm install (or yarn install) installs Webpack that builds the final package.

Alternatively you can download the engine files from the online interpreter instance: he.js and he.wasm. Place the files into the assets directory.

Dev server

Run npm start (or yarn start) to start the development server on localhost:8080. The server automatically reloads the page when you make changes to the source files. Ctrl+C stops the server.

Use the URL http://localhost:8080/play/index.html to access the interpreter.

The development server serves any files found in a directory called "library" in the root of the project. If you create that directory and put test story files there, you can run them using the URL http://localhost:8080/play/index.html?story=/story.hex where "story.hex" is the name of the story file. Note that the leading / character is required.

C Engine

The interpreter engine itself is the official Hugo interpreter engine that has been compiled from C to JavaScript with Emscripten.

In the repository's "he" directory hejs.c contains most of HugoJS-specific C code. It's mainly responsible for communication between the engine and the user interface. C project setup is at the start of heheader.h. There are other minor changes here and there in other C files. The changes are contained in #if defined __EMSCRIPTEN__ directives.

If you make changes to the C interpreter, you need to run the npm run compile (or yarn compile) command to regenerate the JS files using a Docker image that has Emscripten pre-installed. You need to first install Docker to do this.

User Interface

The JavaScript user interface sources are in the src directory.

  • index.js: loads the necessary files and bootstraps the system
  • hugo.js: HugoJS-specific code
  • opcodes.js: special community-extended Hugo opcodes

Haven is the actual JavaScript interpreter that handles the game output. It's included as a git submodule.

Development Scripts

The command npm start (or yarn start) starts Webpack in watch mode (recompiles every time source files change.)

To build the project for deployment use npm run build (or yarn build). Webpack creates a directory called "dist" where it copies necessary files and minifies the scripts. The build script creates a package of the files for deployment.

npm run compile (or yarn compile) compiles the C interpreter into JavaScript.

npm run lint (or yarn lint) runs the source files through ESLint and checks that the coding style is consistent.