Is it possible to combine different modularity systems in Node.js?

Yes, it is possible. Node.js supports coexistence of CommonJS (require()) and ES modules (import) in a single project, but there are nuances.

• By default: Node.js interprets .js files as CommonJS.
• ES modules: To use ES modules, you need to either:
  • Use the .mjs file extension.
  • Specify "type": "module" in the package.json file (then .js will become ES modules, and for CommonJS, .cjs is needed).
• Interaction:
  • ES modules can import CommonJS modules using the syntax import module from 'commonjs-module';.
  • CommonJS cannot directly use import. To import ES modules from CommonJS, dynamic import() or a wrapper is required.

// commonjs.js
module.exports = {
  message: 'Hello from CommonJS'
};

// esmodule.mjs
import commonjsModule from './commonjs.js'; // ES module imports CommonJS

console.log(commonjsModule.message);

// To import an ES module from CommonJS:
// const importESModule = async () => {
//   const esModule = await import('./esmodule-to-import.mjs');
//   console.log(esModule.data);
// };
// importESModule();

// esmodule-to-import.mjs
export const data = 'Hello from ES module';

Combining them requires caution, especially when importing from CommonJS into ES modules and vice versa, to avoid issues with asynchronous operations and export/default compatibility.