Express Module #54

Question 1

What is Express.js? What is it used for?

Answer 1

Express. js is a Node. js web application server framework, designed for building single-page, multi-page, and hybrid web applications. It is the de facto standard server framework for node. … js framework for quickly creating dynamic end-to-end REST APIs.

Question 2

Making a webserver was a dozen or so lines of code using vanilla node.js. Using express it’s only 4 lines. What are those lines?

Answer 2

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

app. get(‘/’, (req, res) => res.send(‘Hello World!’))
app. listen(3000, () => console.log(‘Server ready’))

Question 3

There is a method for every HTTP verb: get( ), post( ), put( ), delete( ), patch( ): How are they written? Hint: they all use the same syntax.

Answer 3

app. get(‘/’, (req, res) => { /* / })
app. post(‘/’, (req, res) => { / / })
app. put(‘/’, (req, res) => { / / })
app. delete(‘/’, (req, res) => { / / })
app. patch(‘/’, (req, res) => { / */ })

Question 4

The HTTP Verbs accept a callback function. How does that look?

Answer 4

(req, res) => res.send(‘Hello World’)

Question 5

What objects are returned from the (req, res) => res.send(‘Hello World’) callback

Answer 5

Request and response objects

Request is the HTTP request. It gives us all the request information, including the request parameters, the headers, the body of the request, and more.

Response is the HTTP response object that we’ll send to the client.

What we do in this callback is to send the ‘Hello World!’ string to the client, using the Response.send() method.

Question 6

What are a few things that are held in the request?

Answer 6

These all seemed fairly self explanatory...
.app 	
.baseUrl 	
.body 	
.cookies 	
.hostname 	
.ip 	
.method 	
.params 	
.path 	
.protocol 	
.query 	
.secure 	
.signedCookies 	
.xhr

Question 7

How do you return query string parameters (‘?’, ‘&’) you see these all the time in urls.

Answer 7

By populating the Request.query object
Example, look at the console.log expression.

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

app.get('/', (req, res) => {
console.log(req.query)
})

app.listen(8080)

Question 8

What happens if there aren’t any query parameters?

Answer 8

Then it returns an empty object

Question 9

What’s the appropriate loop to use on an empty query parameters object or any empty object?

Answer 9

The for in loop. In this situation, it looks like this:

for (const key in req.query) {
console.log(key, req.query[key])
}

Question 10

** How can you retrieve the POST query string parameters using express? And what are they most commonly used for?

Answer 10

POST query parameters are sent by HTTP clients for example by forms, or when performing a POST request sending data.

How can you access this data?

If the data was sent as JSON, using Content-Type: application/json, you will use the express.json() middleware:

const express = require('express')
const app = express ( )
app.use(express.json( )

Question 11

How would you send an empty response (without a body)

Answer 11

res.end( )

Question 12

How do you set the HTTP response header?

Answer 12

Use the Response.status():
Which actually looks like this i action?

res.status(404).end()
or
res.status(404).send(‘File not found’)

res.status(404).end()
or
res.status(404).send(‘File not found’)

Question 13

What method sends a JSON response?

Answer 13

You can send JSON to the client by using Response.json(), a useful method.

It accepts an object or array, and converts it to JSON before sending it:

res.json({ username: ‘Flavio’ })

Question 14

How are cookies managed? That is to say which method?

Answer 14

Use the Response.cookie() method to manipulate your cookies.

Examples:

res.cookie(‘username’, ‘Flavio’)

domain The cookie domain name
expires Set the cookie expiration date. If missing, or 0, the cookie is a session cookie
httpOnly Set the cookie to be accessible only by the web server
maxAge Set the expiry time relative to the current time, expressed in milliseconds
path The cookie path. Defaults to ‘/’
secure Marks the cookie HTTPS only
signed Set the cookie to be signed
sameSite Value of SameSite

Question 15

How can a cookie be cleared

Answer 15

res.clearCookie(‘username’)

Question 16

How are HTTP headers accessed?

Answer 16

You can access all the HTTP headers using the Request.headers property:

app.get(‘/’, (req, res) => {
console.log(req.headers)
})

Question 17

If you want or need to modify a header for a response?

Answer 17

You can change any HTTP header value using Response.set():

res.set(‘Content-Type’, ‘text/html’)

There is a shortcut for the Content-Type header, however:

res.type('.html')
// => 'text/html'

res.type('html')
// => 'text/html'

res.type('json')
// => 'application/json'

res.type('application/json')
// => 'application/json'

res.type('png')
// => image/png:

Question 18

How would you set up a redirect?

Answer 18

Redirects are common in Web Development. You can create a redirect using the Response.redirect() method:

res.redirect(‘/go-there’)

This creates a 302 redirect.

A 301 redirect is made in this way:

res.redirect(301, ‘/go-there’)

You can specify an absolute path (/go-there), an absolute url (https://anothersite.com), a relative path (go-there) or use the .. to go back one level:

res. redirect(‘../go-there’)
res. redirect(‘..’)

You can also redirect back to the Referer HTTP header value (defaulting to / if not set) using

res.redirect(‘back’)

Question 19

What is routing as it pertains to a webserver?

Answer 19

Routing is the process of determining what should happen when a URL is called, or also which parts of the application should handle a specific incoming request.

This creates a route that maps accessing the root domain URL / using the HTTP GET method to the response we want to provide.

Question 20

What if you wanted to utilize dynamic server-side html templates?

Answer 20

npm install pug

const express = require("express")
const app = express()
app.set("view engine", "pug")

To get all of the deets on PUG go to:
https://pugjs.org/api/express.html

Question 21

What’s the process for creating a page?

Answer 21

Create an about view:

app.get(“/about”, (req, res) => {
res.render(“about”)
})

and the template in views/about.pug:

p Hello from Flavio

This template will create a p tag with the content Hello from Flavio.

You can interpolate a variable using

app.get(“/about”, (req, res) => {
res.render(“about”, { name: “Flavio” })
})

Using this:

p Hello from #{name}

To get all of the deets on PUG go to:
https://pugjs.org/api/express.html

Question 22

How would you expose images and css at the root level?

Answer 22

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

app.use(express.static(‘public’))

/* … */

app.listen(3000, () => console.log(‘Server ready’))

If you have an index.html file in public/, that will be served if you now hit the root domain URL (http://localhost:3000)

Question 23

What function do sessions perform?

Answer 23

To identify users. When implemented, every user of your API or website will be assigned a unique session, and this allows you to store the user state.

Question 24

How are sessions for express installed?

Answer 24

npm install express-session

and once you’re done, you can instantiate it in your application with

const session = require(‘express-session’)

This is a middleware, so you install it in Express using

const express = require('express')
const session = require('express-session')

const app = express()
app.use(session({
  'secret': '343ji43j4n3jn4jk3n' //add a random string here
}))

Question 25

Finally FORMS!!! How can you extract data that is in a POST request body.

Answer 25

To extract it, you will need to use the express.urlencoded() middleware, provided by Express:

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

app.use(express.urlencoded())

Now, you need to create a POST endpoint on the /submit-form route, and any data will be available on Request.body:

app.post('/submit-form', (req, res) => {
  const username = req.body.username
  //...
  res.end()
})

Don’t forget to validate the data before using it, using express-validator.