js-oop-class-inheritance-intro.js

// we can declare multiple objects and give them different values for the same properties, 
// which means we have to repeat the same process for every next person

// Class - template for creating objects of new custom type
// In simple English, create just one object and be able to reuse it as a blueprint for all the others 
// --------------------------------------------------------

// To create a class all we need is a class keyword followed by an identifier (a name we gave to the class) 
// and a block of code in between the curly {} braces.

// --------------------------------------------------------

// - Camel case but the FIRST LETTER is typically uppercase (Person, Book, Author)
// - Name is typically SINGULAR (Book, not Books)

// OOP Class
class Person {
  constructor (name, age, country) {
    this.name = name;
    this.age = age;
    this.country = country;
    // A method could also be defined like this
    // although that would defeat the purpose
    // for having a special syntax to define methods
    // this.sayAge = function () {
    //   console.log('I am ' + this.age + ' years old');
    // }
    this.sayHappyBirthday = sayHappyBirthday;
  }
  getAge () {
    console.log(`${this.name} is ${this.age} years old.`);
  }

  greet () {
    console.log('Hello!');
  }

  getName () {
    console.log(`My name is ${this.name}.`);
  }
}

const sayHappyBirthday = function () {
  console.log(`Happy Birthday ${this.name}!`);
};

sayHappyBirthday(); // Happy Birthday undefined


const anaPerson = new Person('Ana', 26, 'Brazil');
const tomasPerson = new Person('Tomas', 28, 'Argentina');

// anaPerson.greet();
// anaPerson.getName();
// anaPerson.getAge();
// anaPerson.sayHappyBirthday();

console.log('----------------------------');

// tomasPerson.greet();
// tomasPerson.getName();
// tomasPerson.getAge();
// tomasPerson.sayHappyBirthday();

console.log('----------------------------');

// CONTRUCTOR: The constructor method is a special method for creating and initializing an object created with a class. 
// There can only be one special method with the name “constructor” in a class.
// In the constructor, "this" refers to the new object created.
// In simple English, the constructor is a method which is used to create the new instances, 
// new objects being created based on the class.

// ------------------------------
// EXTENDS: Using the keyword extends we can add one more layer of abstraction. 
// We can create a new class that will have all the attributes and methods of another class (+ probably some of their own), 
// and for that we will use the keyword "extends". This is known as INHERITANCE.

class Student extends Person {
  constructor (name, age, country, course) {
    // `super` refers to the constructor of the parent (Person)
    // with super Student gets all the attributes and methods of the Person class
    super(name, age, country);

    // course is a new property, only characteristic for student
    this.course = course;
  }

  complainAboutClass () {
    console.log('I wish the pace is slower...');
  }

  graduate (howManyProjects) {
    if (howManyProjects >= 3) return { didGraudate: true, message:`${this.name} successfully graduated.` }
     
    else return { didGraduate: false, message: `Keep grinding, my friend, you are almost there.` }
  }
}

const stefanStudent = new Student('Stefan', 29, 'Montenegro', 'Web Dev');

stefanStudent.greet();
stefanStudent.getName();
stefanStudent.getAge();
stefanStudent.complainAboutClass();
stefanStudent.graduate(2).message;

// const arrayIsInstanceOfArrayClass = {} instanceof Array;
// console.log(arrayIsInstanceOfArrayClass);

console.log(`Is Stefan instance of the Person class? -> ${stefanStudent instanceof Person}`);
console.log(`Is Stefan instance of the Student class? -> ${stefanStudent instanceof Student}`);

console.log(`Is Ana instance of the Person class? -> ${anaPerson instanceof Person}`);
console.log(`Is Ana instance of the Student class? -> ${anaPerson instanceof Student}`);

// Doesnt work
// since ana is a person but not a student
// anaPerson.complainAboutClass();