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Вивчайте Overriding | Inheritance
Object-Oriented Programming in JavaScript

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Overriding

Overriding Methods

In the previous chapter, we redefined the constructor for the daughter class. If there are some methods in the parent class that you want to be different in the daughter’s, you can simply write it again with another function's body:

class Rectangle {
height;
width;
constructor(height, width) {
this.height = height;
this.width = width;
console.log('Rectangle created');
}
rotate() {
side = this.width;
this.width = this.height
this.height = side;
console.log('Now rectangle has width', this.width, 'and height', this.height);
}
}

class Square extends Rectangle{
constructor(size){
super(size, size);
console.log('Square created');
}
rotate() {
console.log('Rotating square does not change it');
}
}

square = new Square(5);
square.rotate();
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class Rectangle { height; width; constructor(height, width) { this.height = height; this.width = width; console.log('Rectangle created'); } rotate() { side = this.width; this.width = this.height this.height = side; console.log('Now rectangle has width', this.width, 'and height', this.height); } } class Square extends Rectangle{ constructor(size){ super(size, size); console.log('Square created'); } rotate() { console.log('Rotating square does not change it'); } } square = new Square(5); square.rotate();
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Here, if you rotate the square, nothing changes, so we'll override this function to only output the message, not change the sides.

In case if you want to use methods from parent’s class, use super keyword again. Let's use increase() method from Rectangle class inside increaseTwice() from Square class.

class Rectangle {
height;
width;
constructor(height, width) {
this.height = height;
this.width = width;
console.log('Rectangle created');
}
increase(num) {
this.width *= num;
this.height *= num
console.log('Now figure has width', this.width, 'and height', this.height);
}
}

class Square extends Rectangle{
constructor(size){
super(size, size);
console.log('Square created');
}
increaseTwice() {
super.increase(2);
}
}

square = new Square(5);
square.increase(4);
square.increaseTwice();
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class Rectangle { height; width; constructor(height, width) { this.height = height; this.width = width; console.log('Rectangle created'); } increase(num) { this.width *= num; this.height *= num console.log('Now figure has width', this.width, 'and height', this.height); } } class Square extends Rectangle{ constructor(size){ super(size, size); console.log('Square created'); } increaseTwice() { super.increase(2); } } square = new Square(5); square.increase(4); square.increaseTwice();
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Завдання

Swipe to start coding

Let's place our Figures in the boxes. Add to the parent's class function box(), which outputs the message I am a Rectangle, and I need a box of size won h, where w and h are width and height of the current Rectangle. Then override this function in Square class, so it outputs the message: I am a Square, and I need a box of size son s, and s is a length of square's side.

Create Rectangle and Square objects and call box() method for them.

Рішення

// box() for the Rectangle
box() {
console.log('I am a Rectangle, and I need a box of size',this.width, 'on', this.height);

// box() for the Sqaure
box() {
console.log('I am a Square, and I need a box of size', this.width, 'on', this.height);

Overriding attributes

Inside the daughter's class, we can refer to any attributes and methods of the parent's class. In general, there is no sense to override attributes because you can refer them directly from the parent's class. The exception is private attributes: they are accessible only inside the current class, that's why you can't override them.

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Секція 4. Розділ 3
class Rectangle {
height;
width;
constructor(height, width) {
this.height = height;
this.width = width;
console.log('Rectangle created');
}
// add your method

}

class Square extends Rectangle{
constructor(size){
super(size, size);
console.log('Square created');
}
// add your method
}

// create objects and call the method .box()
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