Introduction

Prior to the introduction of ECMAScript Modules, the most widely-used module format in JavaScript was CommonJS. The majority of modules on npm are published as CommonJS due to its longstanding support in Node.js, so it's important that build tools can consume CommonJS modules for compatibility reasons. The same is true for JavaScript produced by build tools: many applications need to run in environments like Node.js, which often requires generating bundles in the CommonJS format.

The Test

This test checks to see if each build tool is capable of generating JavaScript bundles that use the CommonJS format. It bundles an entry module that depends on a utils module and a third dynamically-imported exclaim module. The dynamic import can be approximated in CommonJS using an inline require() call.

index.js

import { logCaps } from './utils.js';

// example dynamic import:
async function main() {
  const { exclaim } = await import('./exclaim.js');
  logCaps(exclaim('This is index'));
}
main();

utils.js

export function logCaps(msg) {
  console.log(msg.toUpperCase());
}

exclaim.js

export function exclaim(msg) {
  return msg + '!';
}

The result of bundling index.js should be two JavaScript bundles in CommonJS format: one containing the code from index.js and utils.js, and another with the contents of exclaim.js. The main() function in the first bundle should now contain a dynamic require() call that loads and executes the second bundle.