Architecture and setup of a basic Express application

Express:

  • A framework for building web servers in Node.js.
  • Reads and interprets HTTP requests from clients.
  • Passes a request through functions (middleware) to process the request.
  • Responds to a client with information and data resolutions.

Architecture:

Express combines middleware to modify request data

express() - is the top-level function that creates the Express application and allows access to the 4 Express objects:

  1. Application - app - Exposes the methods to handle HTTP requests, allows configuration of middleware and much more.
  2. Request - req - An object with properties describing the request from a client (url, domain, host, port, headers, body, etc. ) - MDN.
  3. Response - res - An object with properties describing the response sent to a client from the server -> It includes methods for handling routing, setting the status/headers and formatting the response. - MDN
  4. Router - Creates modular route handlers. Referred to as a mini-app. More

Response Methods:

  • res.download()
  • res.end()
  • res.json()
  • res.jsonp()
  • res.redirect()
  • res.render()
  • res.send()
  • res.sendFile()
  • res.sendStatus()
Express SETUP
  1. create a new project directory
  2. inside new directory -> npm init
  3. create a new file inside new directory -> app.js

  4. create a script in package.json:

    "script": {
"start": "node app.js"
}
  5. npm install express

  6. In app.js add to top of file:

    const express = require('express');

  7. Invoke the Express function and assign it to app:

    const app = express();

  8. Test the root route -> create a function:

    app.get('/', (req, res) => {
 res.send('Hello World!');
});

  9. Create a listening function:

    app.listen(8000, () => {
 console.log('Express server is listening on port 8000!');
});
  10. npm start - Go to localhost:8000 to see 'Hello World!"

The complete app.js looks like this:

const express = require('express');
const app = express();

app.get('/', (req, res) => {
  res.send('Hello World.');
});

app.listen(8000, () => {
  console.log('Express server is listening on port 8000!');
});