Beginner Node.js

[dangvanthanh]

Beginner Node.js

• [x] Understanding Async Programming
• [x] Node.js Server
• [x] Using Databases
• [x] The Request Modules
• [x] Authentication
• [x] Unit Testing
• [x] Debugging
• [x] Security

[dangvanthanh]

Understanding Async Programming

Synchronous Programming

const fs = require('fs')

let content

try {
  content = fs.readFileSync('file.md', 'utf-8')
} catch (e) {
  console.log(e)
}

console.log(content)

Asynchronous programming in Node.js

const fs = require('fs')
console.log('Start reading a file')

fs.readFile('file.md', 'utf-8', function (err, content) {
  if (err) {
    console.log('Error happened during reading the file')
    return console.log(err)
  }

  console.log(content)
})

[dangvanthanh]

Node.js Server

The http module for Node.js server

const http = require('http')
const port = 3000

const requestHandler = (req, res) => {
  if (req.url === '/') {
    res.end('Welcome')
  }

  if (req.url === '/hello') {
    res.end('Hello')
  }
}

const server = http.createServer(requestHandler)

server.listen(port, err => {
  if (err) {
    return console.log('Something bad happened', err)
  }

  console.log(`Server is listening on ${port}`)
})

The http module is very low-level. Creating a complex web application web using the snipper above is very time-consuming. This is a reason why we usually pick a framework with for our project. The popular framework.

• Express
• Hapi
• Koa

Express

A sample using Express and Pug. The first, we need install Express and Pug:

$ npm install express --save
$ npm install pug --save

Directory Structure

|__ index.js
|__ views
   |__ index.pug
   |__ hello.pug

Populate index.js such as:

const path = require('path')
const express = require('express')
const app = express()
const port = 3000

app.set('view engine', 'pug')
app.set('views', path.join(__dirname, 'views'))

app.get('/', (req, res) => {
  res.render('index', {
    title: 'Template',
    message: 'Express and Pug Template'
  })
})

app.get('/hello', (req, res) => {
  res.render('hello', {
    title: 'Hello',
    name: 'Dang Van Thanh'
  })
})

app.listen(port, (err) => {
  if (err) {
    return console.log('Something bad happened', err)
  }

  console.log(`Server is listening on ${port}`)
})

Nunjucks

Nunjucks is a rich and powerful templating language for JavaScript. And Nunjucks familiar HTML than Pug.

$ npm install nunjucks --save

const nunjucks = require('nunjucks')
const express = require('express')

nunjucks.configure('views', {
  express: app,
  autoescape: true
})

app.set('view engine', 'html')

app.get('/', (req, res) => {
  res.render('index.html')
})

Static Files in Express

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

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

[dangvanthanh]

Using Databases in Node.js

You can set up a Node.js application databases and using it. Below some way you can storing data:

Storing data in global variable

const users = []

app.post('/users', (req, res) => {
  users.push({
    name: 'Dang Van Thanh',
    age: 30
  })

  res.send('Successfully registered')
})

Using this methods might be problematic for several reasons:

• RAM is expensive
• Memory resets each time you restart application
• End up with stack overflow if you don't cleanup

Storing data in a file

const fs = require('fs')

app.post('/users', (req, res) => {
  fs.appendToFile(
    'user.txt',
    JSON.stringify({ name: 'Dang Van Thanh', age: 30 }),
    err => {
      res.send('Sucessfully registered')
    }
  )
})

This method still has a couple of flaws:

• Updating and Deleting
• No easy way to access in parallel (system-wide locks will prevent from writing)
• Scale application is complex

Real databases

SQL

• MySQL
• PostgreSQL

NoSQL

• MongoDB
• DynamoDB

Node.js and PostgreSQL

Node PostgreSQL Documentation

$ npm install pg --save

You can interact with PostgreSQL via Node.js such as:

const express = require('express')
const { Client } = require('pg')
const connectionString = 'postgres://dangvanthanh@localhost/learning_objectives'
const client = new Client({
  connectionString: connectionString
})
const app = express()
const port = 3000

// Insert record to `users` table in `learning_objectives` database
app.post('/users', (req, res, next) => {
  let user = {}

  user.name = 'Dang Van Thanh '
  user.age = 30

  client.connect()

  client.query(
    'INSERT INTO users (name, age) VALUES ($1, $2);',
    [user.name, user.age],
    (err, result) => {
      if (err) {
        console.log(err)
      }

      res.send(200)
    }
  )
})

// Query all records from `users` table in `learning_objectives` database
app.get('/users', (req, res, next) => {
  client.connect()

  client.query('SELECT name, age FROM users;', [], (err, result) => {
    if (err) {
      console.log(err)
    }

    res.json(result.rows)
  })
})

app.listen(port, err => {
  if (err) {
    return console.log('Something bad happened', err)
  }

  console.log(`Server is listening on ${port}`)
})

[dangvanthanh]

The Request Module

What's HTTP

HTTP stands for Hypertext Transfer Protocol. HTTP functions as a request-response protocol in the client-server computing model

HTTP Status Codes

Status Codes	Description	Most Common
1xx	Informational
2xx	Success	Success codes are 200 OK, 201 Created and 204 No Content
3xx	Redirection	Redirection codes are 301 Moved Permanently, 304 Not Modified
4xx	Client Error	Client error codes are 400 Bad Request, 401 Unauthorized, 403 Forbidden, 404 Not Found, 409 Conflict
5xx	Server Error	Server error codes are 500 Internal Server Error, 503 Service Unavailable

Using the Node.js Request Module

Create a small Express application that can render the current weather conditions based on city names using AccuWeather API

const path = require('path')
const nunjucks = require('nunjucks')
const express = require('express')
const rq = require('request-promise')
const app = express()
const port = 3000

nunjucks.configure('views', {
  express: app,
  autoescape: true
})

app.set('view engine', 'html')
app.set('views', path.join(__dirname, 'views'))
app.use('/static', express.static('public'))

app.get('/:city', (req, res) => {
  rq({
    uri: 'http://apidev.accuweather.com/locations/v1/search',
    qs: {
      q: req.params.city,
      apiKey: 'hoArfRosT1215'
    },
    json: true
  })
    .then(data => {
      const city = {
        name: data[0].EnglishName,
        geo: {
          lat: data[0].GeoPosition.Latitude,
          long: data[0].GeoPosition.Longitude
        }
      }

      res.render('index.html', { city: city } )
    })
    .catch(err => {
      console.log(err)
      res.render('error.html')
    })
})

app.listen(port, err => {
  if (err) {
    return console.log('Something bad happened', err)
  }

  console.log(`Server is listening on ${port}`)
})

[dangvanthanh]

Authentication

[dangvanthanh]

Unit Testing

[dangvanthanh]

Debugging

[dangvanthanh]

Security