nodejs-webserver

simple node.js webserver for learning some basic concepts

first steps: use someone else's webserver

• open gitbash (or terminal on mac)

• git clone https://github.com/techtabor/nodejs-webserver.git

• cd word-associations

• npm install: this will install dependencies, namely express npm package

  • what is express?

• () => {} is a shorthand for function() {} javascript function definition

• type node getPublicAPI.js in your terminal

• it gets the response from a publicly available webserver

• what is the first param of the https.get function?

• what is the second param of the https.get function?

  • it is a so called callback function
  • callback: it will be CALLED when the main part of the function has been executed and returned BACK its result
  • callback functions in javascript are a solution to handle asynchronous function calls
  • the https.get function is asynchronous, it may run parallel with other commands. Still, you want to handle the result exactly right after it is received. So you put in the callback function.
  • it is called after: test it with using the result inside the callback function

  var handleRequestResult = (res) => {
    console.log(result)
    res.on('data', (d) => {
      console.log('BODY in result of https request: ' + d)
    })
  }
  
  var result = https.get('https://api.ipify.org', handleRequestResult)

  • if you would try to handle the result in a simple, not callback function: it would not work as the handling will be executed sooner than the https get request is received.

  var https = require('https')
  
  var handleRequestResult = (res) => {
    res.on('data', (d) => {
      console.log('BODY in result of https request: ' + d)
    })
  }
  
  var result = https.get('https://api.ipify.org')
  
  handleRequestResult(result)

second steps: create your own webserver

• create app.js file with the following

var express = require('express')
var app = express()

app.listen(3000, () => {
  console.log('nodejs-webserver app listening on port 3000')
})

• type node app.js in your terminal
• what do you see if you open localhost:3000 in your browser?
• what does localhost mean, what is the corresponding IP-address?
• what does 3000 represent?
  • the number of the port
  • can you change it to any number, e.g. 80?
  • why is the 80 port special?
• stop the webserver (Ctrl + C, Ctrl + C), then refresh the page in your browser
• change the used port to 2016

var defaultPort = 2016

app.listen(defaultPort, () => {
  console.log('nodejs-webserver app listening on port ' + defaultPort)
})

• open localhost:2016
• open localhost:3000
• change port back to 3000
• add response for GET request: add the following to the end of your app.js file

app.get('/', (req, res) => {
  res.send('nodejs-webserver')
})

• what are the two parameters of the app.listen function?
• what happens when you delete the second parameter? Start you server.

app.listen(defaultPort)

• what is the req parameter? add the following line:

app.get('/', (req, res) => {
  console.log(req.headers)
  res.send('nodejs-webserver')
})

• the server should be able to show content on another page: localhost:3000/words.

app.get('/words', (req, res) => {
  res.send('words:')
})

third steps: use your own server

• start your server and get the sent result from another node.js script

var http = require('http')

var httpOptions = {
  hostname: 'localhost',
  port: 3000,
  path: '/title'
}

var handleRequestResult = (res) => {
  res.on('data', (d) => {
    console.log('BODY in result of http request: ' + d)
  })
}

http.get(httpOptions, handleRequestResult)

• run node get.js in another window of your terminal

If you have problems, check previous commits on github, they contain solutions to each step.

more advanced steps

• refactor routing to separate file
• add code for building a chain of associated words and POST it as JSON