ECMAScript modules in node.js

Node.js supports ECMAScript modules for few years now and if you still consider switching from the CommonJS, there are a couple of good arguments for.

First, enabling the module subsystem is as easy as adding

  ...
  "type": "module",
  ...

to the package.json. Then, modules can be exported/imported, both default and named conventions are supported:

// foo.js
function foo(n) {
    return n+1;
}

function bar(n) {
    return n-1;
}

function qux(n) {
    return n-2;
}

export { bar };
export { qux };
export default foo;

// app.js
import foo from './foo.js';
import { bar, qux } from './foo.js';

console.log( foo(5) );
console.log( bar(5) );
console.log( qux(5) );

Modules can reference other modules recursively, the old good CommonJS supports cycles too but here it's even easier:

// a.js
import { b } from './b.js';

function a(n) {
    if ( n > 1 ) {
        console.log( `a: ${n}` );
        return b( n-1 );
    } else {
        return 1;
    }
}

export { a };

// b.js
import { a } from './a.js';

function b(n) {
    if ( n > 1 ) {
        console.log( `b: ${n}` );
        return a( n-1 );
    } else {
        return 1;
    }
}

export { b };

// app.js
import { a } from './a.js';

console.log( a(7) );

Modules support top-level await

// app.js
console.log( await 7 );

And last but not least, modules interoperate with existing infrastructure

// app.js
import http from 'http';
import express from 'express';

var app = express();

app.get('/', (req, res) => {
    res.end( 'hello world');
});

http.createServer( app ).listen(3000, () => {
    console.log( 'started');
});