REST defines a set of conventions for creating HTTP services:

• POST: to create a resource
• PUT: to update it
• GET: to read it
• DELETE: to delete it

Express is a simple, minimalistic and lightweight framework for building web
servers.

// Build a web server
const express = require(‘express’);
const app = express();

// Creating a course
app.post(‘/api/courses’, (req, res) => {
// Create the course and return the course object
resn.send(course);
});

// Getting all the courses
app.get(‘/api/courses’, (req, res) => {
// To read query string parameters (?sortBy=name)
const sortBy = req.query.sortBy;

// Return the courses
res.send(courses);
});

// Getting a single course
app.get(‘/api/courses/:id’, (req, res) => {
const courseId = req.params.id;

// Lookup the course
// If not found, return 404
res.status(404).send(‘Course not found.’);

// Else, return the course object
res.send(course);
});

// Updating a course
app.put(‘/api/courses/:id’, (req, res) => {
// If course not found, return 404, otherwise update it
// and return the updated object.
});

// Deleting a course
app.delete(‘/api/courses/:id’, (req, res) => {
// If course not found, return 404, otherwise delete it
// and return the deleted object.
});

// Listen on port 3000
app.listen(3000, () => console.log(‘Listening…’));

• We use Nodemon to watch for changes in files and automatically restart the
  node process.
• We can use environment variables to store various settings for an application. To
  read an environment variable, we use process.env.

// Reading the port from an environment variable
const port = process.env.PORT || 3000;
app.listen(port);

• You should never trust data sent by the client. Always validate! Use Joi package
  to perform input validation.

• A middleware function is a function that takes a request object and either
  terminates the request/response cycle or passes control to another middleware
  function.

• Express has a few built-in middleware functions:

• json(): to parse the body of requests with a JSON payload

• urlencoded(): to parse the body of requests with URL-encoded payload

• static(): to serve static files

• You can create custom middleware for cross-cutting concerns, such as logging,
  authentication, etc.

// Custom middleware (applied on all routes)
app.use(function(req, res, next)) {
// …
next();
}
// Custom middleware (applied on routes starting with /api/admin)
app.use(‘/api/admin’, function(req, res, next)) {
// …
next();
}

• We can detect the environment in which our Node application is running
  (development, production, etc) using process.env.NODE_ENV and
  app.get(‘env’).
• The config package gives us an elegant way to store configuration settings for
  our applications.
• We can use the debug package to add debugging information to an application.
  Prefer this approach to console.log() statements.
• To return HTML markup to the client, use a templating engine. There are various
  templating engines available out there. Pug, EJS and Mustache are the most
  popular ones.