# OOP in JavaScript

## Creating a JavaScript Object

### `Object.create`

```js
function Book({name, author, year}) {
	const constructor = {
		getTitle: function() {
			return this.name + ' by ' + this.author + ' (' + this.year + ')';
		}
	};
	const book = Object.create(constructor);
	book.name = name;
	book.author = author;
	book.year = year;

	return book;
}

// test
const lastBook = Book({
	name: "Foundation and Earth",
	author: "Isaac Asimov",
	year: 1986
});

console.log(lastBook); // {name: 'Foundation and Earth', author: 'Isaac Asimov', year: 1986}
console.log(lastBook.getTitle()); // Foundation and Earth by Isaac Asimov (1986)
```

### `new` keyword

> PROTOTYPE CHAINING, function object combination

```js
function Book({name, author, year}) {
	this.name = name;
	this.author = author;
	this.year = year;
}

Book.prototype.getTitle = function() {
	return this.name + ' by ' + this.author + ' (' + this.year + ')';
};

// test
const lastBook = new Book({
	name: "Foundation and Earth",
	author: "Isaac Asimov",
	year: 1986
})

console.log(lastBook); // Book {name: 'Foundation and Earth', author: 'Isaac Asimov', year: 1986}
console.log(lastBook.getTitle()); // Foundation and Earth by Isaac Asimov (1986)
```

### `Class` (ECMAScript 2015)

```js
class Book {
	constructor({name, author, year}) {
		this.name = name;
		this.author = author;
		this.year = year;
	}

	getTitle() {
		return this.name + ' by ' + this.author + ' (' + this.year + ')';
	}
}

// test
const lastBook = new Book({
	name: "Foundation and Earth",
	author: "Isaac Asimov",
	year: 1986
})

console.log(lastBook); // Book {name: 'Foundation and Earth', author: 'Isaac Asimov', year: 1986}
console.log(lastBook.getTitle()); // Foundation and Earth by Isaac Asimov (1986)
```

## Subclassing

```js
class BookInterface {
	constructor(author) {
		this.author = author;
	}

	getAuthor() {
		return this.author;
	}
}

class Book extends BookInterface {
	constructor({name, author, year}) {
		super(author);

		this.name = name;
		this.year = year;
	}

	getTitle() {
		return this.name + ' by ' + this.author + ' (' + this.year + ')';
	}
}

// test
const lastBook = new Book({
	name: "Foundation and Earth",
	author: "Isaac Asimov",
	year: 1986
})

console.log(lastBook); // Book {name: 'Foundation and Earth', author: 'Isaac Asimov', year: 1986}
console.log(lastBook.getTitle()); // Foundation and Earth by Isaac Asimov (1986)
```

### Subclassing via `Object.create`

> Object.setPrototypeOf

```js
function BookInterface(author) {
	const constructor = {
		getAuthor: function() {
			return this.author;
		}
	};
	const book = Object.create(constructor);
	book.author = author;
	return book;
}

function Book({name, author, year}) {
	const book = BookInterface(author);

	const constructor = {
		getTitle: function() {
			return this.name + ' by ' + this.author + ' (' + this.year + ')';
		}
	};
	Object.setPrototypeOf(book, constructor);
	book.name = name;
	book.year = year;
	return book;
}

// test
const lastBook = new Book({
	name: "Foundation and Earth",
	author: "Isaac Asimov",
	year: 1986
});

console.log(lastBook); // {name: 'Foundation and Earth', author: 'Isaac Asimov', year: 1986}
console.log(lastBook.getTitle()); // Foundation and Earth by Isaac Asimov (1986)
```

## JavaScript Class

```js
class Book {
  #genre;

  constructor({ name, author, year, genre }) {
    this.name = name;
    this.author = author;
    this.year = year;

    this.#genre = genre;
  }

  static getInfo() {
    return 'Class: Book';
  }

  getTitle() {
    return this.name + ' by ' + this.author + ' (' + this.year + ')';
  }

  get() {
    return this.#getBook();
  }

  getGanre() {
    return this.#genre;
  }

  #getBook() {
    return {
      ...this,
    };
  }
}

// test
const lastBook = new Book({
  name: 'Foundation and Earth',
  author: 'Isaac Asimov',
  year: 1986,
  genre: 'sci-fi',
});

console.log(Book.getInfo());

console.log(lastBook);
console.log(lastBook.getTitle());
console.log(lastBook.get());

console.log(lastBook.getGanre());
```

### Singleton pattern

```js
class Singleton{
	constructor() {
		if (Singleton._instance) {
			Singleton._instance = this;
		}

		return Singleton._instance;
	}

	static getInstance() {
		return this._instance;
	}
}
```