nodejs_require.js

// File: A.js
console.log("In A.js");

class A {
    construtor() {
        //some logic   
    }  
}

module.exports = A;
// Alternatively, with ES6 this would be 'export default A'

/*-------------------*/

//File B.js
console.log("In B.js");

class B {
    constructor() {
        //some logic
    }
}

module.exports = B;

// Alternatively, with ES6 this would be 'export default B'

/*-------------------*/

//File C.js
console.log("In C.js");

class C {
}

module.exports = C;

// Alternatively, with ES6 this would be 'export default C'

/*-------------------*/

//File index.js
const express = require("express");
const A = require("A"); //or import A from 'A';
const B = require("B"); //or import B from 'B';
const routes = require("./routes");
//Notice that we don't import anything from C.js

const app = express();
app.use(routes);
app.listen(3000, () => console.log("Server running on port 3000");