hr_express.md

ExpressJS Instructor Notes

Objectives

• Describe how a client interacts with a server
• Explain what ExpressJS is and why it is useful
• Use middleware in an Express application
• Use middleware with routes and HTTP verbs

How a client interacts with a server?

• What is the flow of information between the client and the server? What are the names and parts?

What is express and why is it useful?

Given the following examples of a web server written with Node http and Express that perform the same tasks

const fs = require('fs')
const http = require('http')

const server = http.createServer(function(request, response) {
  if(request.url === '/logo.png') {
    response.writeHead(200, {'Content-Type': 'image/gif'})

    fs.readFile(__dirname + '/public/logo.png', function(err, data) {
      if(err) console.log(err)

      response.end(data)
    })
  }
  else if (request.url === '/'){
    response.writeHead(200, {'Content-Type': 'text/html' })

    fs.readFile(__dirname + '/public/index.html', function(err, data) {
      if(err) console.log(err)

      response.end(data)
    })
  }
}) // and much more besides

const express = require('express')
const http = require('http')

const app = express()

app.use(express.static('./public'))

app.get('/', function(req, res, next) {
  res.sendFile('./public/index.html')
})

http.createServer(app).listen(3000)
console.log('Express server is listening on port 3000')

• What are the tasks performed?
• What parts are of the process does Express help you with

How do you use middleware in Express?

• What is middleware?
• Why is middleware useful?
• What arguments does a middleware take?
• How is middleware added to an express application?
• What does the following middleware do?

const express = require('express')
const http = require('http')

const app = express()

app.use(function(req,res, next){
  console.log(`Request: ${req.method} at ${req.url}`)
  next()
})

http.createServer(app).listen(3000)
console.log('Express server is listening on port 3000')

• How would you make the middleware only run on a specific route?

How do you use middleware with routes and HTTP verbs?

• What are HTTP verbs? What are some examples?
• What part of the client server communication do they belong in?
• How would you add a middleware the matches a route with a specific HTTP verb?
• Fill in the blank, create the middleware, no need for actual code to handle actions
  • Create a route to get all users
  • Create a route to create a user

const express = require('express')
const http = require('http')

const app = express()

/*
Your code goes here
*/


http.createServer(app).listen(3000)
console.log('Express server is listening on port 3000')