Data structures

Arrays

const courseCodes = ['1DV525', '1DV523', '1DV021']
courseCodes.push('1DV022')
console.log(courseCodes.length) // ➡ 4

MDN Array

Iterator functions

forEach

  let courseCode = ['1DV525', '1DV523', '1DV021']
  courseCode.forEach((node) => {console.log(node)}) // ➡ 1DV525 ➡ 1DV523 ➡ 1DV021

filter

const courseCodes = ['1DV525', '1DV523', '1DV021']
const intCourses = courseCodes.filter((node) => node.charAt(3) === '5' )
console.log(intCourses) // ➡ [ '1DV525', '1DV523' ]

• map
• reduce
• sort
• ...

Rest parameters and the Spread operator (ES2015)

  const registerStudent = function(name, age, ...courses){
    console.log(courses)
  }
  registerStudent('Ellen', 30, '1DV525', '1DV523', '1DV021')
  const courses = ['1DV525', '1DV523', '1DV021', '2DV022']
  registerStudent('Ellen', 30, ...courses)

Ex. Find highest number

  // Math.max syntax: Math.max([value1[, value2[, ...]]])
  const numbers = [2, 5, 2, 5, 10, 3, 1, 5, 7, 8, 3 ,1]
  console.log(Math.max(...numbers)) // ➡ 10

Objects

  const objectLiteral = {}
  console.log(typeof objectLiteral) // ➡ object

With properties and methods

  const student =  {
    name : "Ellen",
    age  : 30,
    greet: function() {
      console.log(this.name + ' is greeting you!')
    }
  }
  student.city = "Växjö"
  student['registered'] = true
  student.greet() // ➡ Ellen is greeting you!

Example

  const courses = [
    { code: '1DV525', students: 55, type: 'distance', url: 'https://github.com/1dv525' },
    { code: '1DV607', students: 104, type: 'campus', url: 'https://github.com/1dv607' },
    { code: '1DV607', students: 67, type: 'distance', url: 'https://coursepress.lnu.se/1dv021'},
    { code: '1DV523', students: 35, type: 'distance', url: 'https://github.com/1dv021' }
  ]

Problem:

Count the number of students taking a distance
learning course using github.com as url

Heavily influenced (stolen) by Arrow functions in JavaScript - What, Why and How - FunFunFunction

Factory pattern

  const createStudent = function(name, age) {
    return {
      name : name,
      age  : age,
      greet: function(){
        console.log(this.name + ' is greeting you!')
      }
    }
  }
  const students = []
  students.push(createStudent('Ellen', 30))
  students.push(createStudent('Peter', 32))
  students.forEach( (student) => {student.greet()})

Constructor pattern

  function Student(name, age) {
    this.name = name
    this.age = age
    this.greet = function(){
      console.log(this.name + ' is greeting you!')
    }
    return this //Default when called with new
  }
  const students = []
  students.push(new Student('Peter', 32))
  students.push(new Student('Ellen', 30))
  students.forEach((student) => {student.greet()})
  console.log(students[0].constructor) // ➡ [Function: Student]

Constructor/Prototpe pattern

  function Student(name, age) {
    this.name = name
    this.age = age
  }
  Student.prototype.greet = function(){
    console.log(this.name + ' is greeting you!')
  }
  const students = []
  students.push(new Student('Peter', 32))
  students.push(new Student('Ellen', 30))
  students.forEach((student) => {student.greet()})

Prototypes

Prototype chain

let person = {
  name: "N.N",
  age: 17,
  greet: function() {console.log(this.name, 'says hi!')}
}
let student = Object.create(person)

Students will be a new object with person as prototype.

"Prototypal inheritance"

"Public" / "Private"

  function Student(name, age) { // "Private"
    this.name = name // "Public"
    this.age = age // "Public"
  }
  Student.prototype.greet = function(){ // "Public"
    console.log(this.name + ' is greeting you!')
  }
  const students = []
  students.push(new Student('Peter', 32))
  students.push(new Student('Ellen', 30))
  students[0].name = "Foo"
  students.forEach((student) => {student.greet()})
`

"Getters" / "Setters"

  function Student(name) {
    this.setName = function(_name){
      // Do fancy validation here
      name = _name
    }
    this.getName = function(){
      return name
    }
    this.setName(name)
  }
  Student.prototype.greet = function(){
    console.log(this.getName() + ' is greeting you!')
  };
  const students = []
  students.push(new Student('Peter', 32))
  students.push(new Student('Ellen', 30))
  students.forEach((student) => {student.greet()})
`

However... there is a better way of doing this...

defineProperty

  function Student(name) {
    Object.defineProperty(this, "name", {
      get: function(){
        return name
      },
      set: function(value) {
        // Fancy validation here
        name = '--'+value+'--'
      }
    })
    this.name = name // Don´t forget
  }
  Student.prototype.greet = function(){
    console.log(this.name + ' is greeting you!')
  }
  const students = []
  students.push(new Student('Peter', 32))
  students.push(new Student('Ellen', 30))
  students.forEach((student) => {student.greet()})
`

Class (ES2015)

  class Student {
    constructor(name) {
      this.name = name // Will call the setter
    }
    greet(){ // Prototype function
      console.log(this.name + ' is greeting you!')
    }
    get name(){ // Shortcut to defineProperty
      return this._name
    }
    set name(value) { // Shortcut to defineProperty
      this._name = '--'+value+'--'
    }
  }
  const students = []
  students.push(new Student('Peter', 32))
  students.push(new Student('Ellen', 30))
  students[0].name = "Johan"
  students.forEach((student) => {student.greet()})

Inheritance

  class Polygon {
    constructor(height, width) {
      this.height = height
      this.width = width
    }
  }
  class Square extends Polygon {
    constructor(sideLength) {
      super(sideLength, sideLength)
    }
    get area() {
      return this.height * this.width
    }
    set sideLength(newLength) {
      this.height = newLength
      this.width = newLength
    }
  }
  var square = new Square(2)

Composition

const supervisor = (state) => ({
  supervise: (student) => {console.log(state.name + ' is supervising ' + student.name + '...')}
})
const examinate = (student) => {
  console.log('Examinating ' + student.name + '...');
}
const student = (name = 'N.N', age = '18') => {
  let state = {
    name,
    age
  }
  return Object.assign(
    state,
    supervisor(state)
  )
}
var mj222sa = student("Nils")
var el222sa = student("Ellen")
el222sa.supervise(mj222sa)

Node.js Modules

greetings.js

  module.exports.sayHelloInEnglish = () => "Hello"
  module.exports.sayHelloInSpanish = () => "Hola"
  module.exports.sayHelloInSwedish = () => "Hej"

app.js

var greet = require('./greetings')
console.log(greet.sayHelloInSpanish()) // ➡ Hola

Export a class

Student.js

  class Student {
    constructor(name) {
      this.name = name
    }
    greet() {
      console.log(this.name + ' is greeting you!')
    }
    get name() {
      return this._name
    }
    set name(value) {
      this._name = '--'+value+'--'
    }
  }
  module.exports = Student

app.js

  var Student = require('./Student')
  console.log(new Student('Ellen', 32))