A TypeScript-based GitHub Action is implemented as a JavaScript action because TypeScript is compiled or bundled into JavaScript before execution by the GitHub Actions runner. JavaScript actions use an action.yml metadata file whose runs.using value specifies a supported Node.js runtime and whose runs.main property identifies the generated JavaScript entry point, commonly a file under dist. This approach allows the action to run directly on supported Linux, Windows, and macOS runners without requiring a separate Docker container. A composite action is intended primarily to combine reusable workflow steps, while a Bash script action is not a distinct metadata action type. Docker container actions are appropriate when a packaged container environment is specifically required. Therefore, a custom action authored in TypeScript should be packaged and distributed as a JavaScript action.

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