Node.js modular express application

1. Simple example.md

To make express web application modular use router factories: Module:

// greet.js
const express = require("express");
module.exports = function (options = {}) {
  // Router factory
  const router = express.Router();
  router.get("/greet", (req, res, next) => {
    res.end(options.greeting);
  });
  return router;
};

Application:

// app.js
const express = require("express");
const greetMiddleware = require("./greet.js");
express()
  .use("/api/v1/", greetMiddleware({ greeting: "Hello world" }))
  .listen(8080);

2. More complicated example.md

Example with services that shows middleware factory advantages. Module:

// greet.js
const express = require("express");
module.exports = function (options = {}) {
  // Router factory
  const router = express.Router();
  // Get controller
  const { service } = options;
  router.get("/greet", (req, res, next) => {
    res.end(service.createGreeting(req.query.name || "Stranger"));
  });
  return router;
};

// app.js
const express = require("express");
const greetMiddleware = require("./greet.js");
class GreetingService {
  constructor(greeting = "Hello") {
    this.greeting = greeting;
  }
  createGreeting(name) {
    return `${this.greeting}, ${name}!`;
  }
}
express()
  .use(
    "/api/v1/service1",
    greetMiddleware({
      service: new GreetingService("Hello"),
    })
  )
  .use(
    "/api/v1/service2",
    greetMiddleware({
      service: new GreetingService("Hi"),
    })
  )
  .listen(8080);

Testing

When accessing http://<hostname>:8080/api/v1/service1/greet?name=World the output will be Hello, World and accessing http://<hostname>:8080/api/v1/service2/greet?name=World the output will be Hi, World.