CommonJS Modules

CommonJS (opens new window) module loader, the require() function, is also available on ES4X. It is important to know that this loader is not the same as nodejs loader. It is a fork of npm-jvm (opens new window) that is ES4X specific.

Specific differences

Modules can be loaded from the file system or from within jar files. The loading process always goes over the Vert.x FileSystem (opens new window).

ESM import syntax

Editors such as Visual Studio Code (opens new window) prefers to auto complete import statement using ESM syntax. Of course this syntax is not compatible with commonjs, however the loader will attempt to adapt the import statements to commonjs if possible.

Consider the following example:

import { TestSuite } from '@vertx/unit';

const suite = TestSuite.create("the_test_suite");
// ...
suite.run();

This code is not compatible with commonjs, however the require() function will transform the source code to:

const TestSuite = require('@vertx/unit').TestSuite;

const suite = TestSuite.create("the_test_suite");
// ...
suite.run();

WARNING

Even though import statement will be adapted, exports are not. All exports must use the commonjs format:

module.exports = { /* ... */ }