entry-script

Write a Node.js script whose main() only runs when it's the entry point, so tests can import it without side effects.

import { EntryScript } from 'entry-script';

export class Greet extends EntryScript {
    public override async main([name = 'world']: string[]): Promise<void> {
        console.log(`Hello, ${name}!`);
    }
}

export default new Greet();

node greet.js Ada prints Hello, Ada!. A test that imports Greet gets the class, and nothing runs until it calls main() itself.

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Features

• No side effects on import: a script's work happens in main(), which only runs when Node was started with that file.
• Testable: construct the class with test doubles, and call main() with the arguments you want.
• Arguments without the noise: main() receives the command-line arguments only, without the Node binary and script path.
• Class or instance: export an instance and implement main, or export the class and implement static main.
• With dependency injection: haywire-launcher builds the script from a Haywire container, only when it runs.

Compared to

• if (import.meta.url === pathToFileURL(process.argv[1]).href), or CommonJS's require.main === module, checks the same thing by hand in every script, and breaks when the entry point is a different file that re-exports the script (like a bin.mjs shim).
• Node.js's newer import.meta.main is only true in the entry module itself, so a script re-exported by a shim still needs care. entry-script finds the entry point's default export, wherever it was defined.