Intro to Express

Create a New Express Project

mkdir starlight
cd starlight
touch app.js
npm init -y
npm i express

Set Up a Basic Express Server

In app.js:

const express = require('express')

const app = express()
const port = 3000

app.listen(port, () => {
  console.log(`Server listening on port ${port}`)
})

Then start the server with:

node app.js

This starts a server on port 3000 and… does nothing.

GET Routes

To respond to GET requests, use the app.get method:

app.get('/', () => {
  console.log('Index route / hit')
})

Web servers are long-running processes. If you make any changes to the code, you'll need to stop the server with Control-c and then start it again with node app.js.

Once you're restarted the server, visit localhost:3000 in your web browser, you should see the text "Index route / hit" in your terminal but nothing in your web browser.

To send a response back to the browser, you can use res.send:

app.get('/', (req, res) => {
  console.log('Index route / hit')
  res.send('Hello world')
})

Or return some HTML:

app.get('/', (req, res) => {
  console.log('Index route / hit')
  res.send('<h1>Hello world</h1>')
})

Restart the server and reload localhost:3000. You should now see the text Hello world in the web browser.

NOTE You can only send one response for every request. If you try to send multiple responses you'll get an error.

req & res

• req is an object containing information about the HTTP request (HTTP method, request body, ip address, query params, etc).

• res is an object representing the HTTP response, which is used to send something back to the client.

POST Routes

To handle form submissions, you have to tell Express to parse the incoming form data using the urlencoded middleware. In the POST route, the form data is available in req.body.

app.use(express.urlencoded({ extended: true }))

app.post('/', (req, res) => {
  res.send(req.body)
})

Route Parameters

To capture the value of the dynamic path segment of the URL, define a GET route with a route parameter (note the : in :bookID). The value of the route parameter can be accessed in the req.params object.

app.get('/books/:bookID', (req, res) => {
  console.log(req.params.bookID)
})

You can define as many route params as you want as long as they're named differently:

app.get('/hello/:firstname/:lastname', (req, res) => {
  console.log(req.params)
  res.send(`Hello ${req.params.firstname} ${req.params.lastname}!`)
})

In your browser, go to localhost:3000/hello/taylor/hebert.

Query Parameters

To get the values in a query string, use req.query.

// localhost:3000/books?page=2&limit=12
app.get('/books', (req, res) => {
  console.log(req.query)
})

nodemon

Restarting the server manually any time you want to test changes to the code is tedious. Using an npm package called nodemon, you can automate this process and streamline your workflow.

npm i -g nodemon

The -g/--global flag installs an npm package so that any project can use it. NOTE If you're using nvm, globally installed packages will only be available for the version of node you were using when you installed the package.

Start your server with:

nodemon

Nodemon will look for the "main" property in your package.json and execute that .js file. If you have "app.js" as "main" in package.json then the above command is equivalent to:

nodemon app.js

Nodemon will watch for any changes you to make to your code and restart the server automatically.