The correct options are JavaScript actions created with Node.js work across Ubuntu, Windows, and macOS GitHub-hosted runners, JavaScript actions run in the runner process and rely on tools that already come with the runner image, and Using the GitHub Actions Toolkit libraries can speed up authoring and testing of your action.

JavaScript actions use the Node.js runtime that is available on GitHub-hosted runners, which lets the same action run on Ubuntu, Windows, and macOS. Cross platform behavior is achievable when you avoid operating system specific commands and file path assumptions and when you rely on the runtime and APIs provided by GitHub Actions.

These actions execute directly on the runner machine rather than inside a container, which means they can call the software and utilities that come preinstalled on the runner image. This reduces setup time and leads to predictable behavior that matches the tools and versions supplied by the image.

Using the GitHub Actions Toolkit libraries can speed up authoring and testing of your action because the official packages provide helpers for inputs and outputs, logging, error handling, executing commands, and calling the GitHub API. This reduces boilerplate and makes it easier to write reliable actions and to test them locally.

It is best practice to include compiled binaries alongside your JavaScript action so setup is easier and results are consistent is incorrect because JavaScript actions should be distributed as bundled JavaScript rather than platform specific binaries. The recommended practice is to compile your source and dependencies into a single distributable file and commit the generated distribution so the runner can execute it with the Node.js runtime that it already provides.

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