Polymorphism Principle

Polymorphism is one of the 4 main OOP principles. It's the ability to take many forms.

Runtime Polymorphism

Runtime Polymorphism occurs in function overriding .

This means that the base class has a function that's being overwritten in the children classes:

class Figure { // base class method that'll be overwritten: calcArea() { return 0; } } class Square extends Figure { constructor(sideValue) { super(); this.side = sideValue; } // overwriting base method: calcArea() { return this.side * this.side; } } class Triangle extends Figure { constructor(aVal, bVal, cVal) { super(); this.a = aVal; this.b = bVal; this.c = cVal; } // overwriting base method: calcArea() { // Get triangles side: let a = this.a; let b = this.b; let c = this.c; // Calculate Area let p = (a + b + c) / 2; let area = Math.sqrt(p * (p - a) * (p - b) * (p - c)); return area; } } let square = new Square(2); console.log("Square Area = " + square.calcArea()); let triangle = new Triangle(3, 4, 5); console.log("Triangle Area = " + triangle.calcArea());

Output:

Square Area = 4 Triangle Area = 6

The function calcArea in Figure class is overwritten by Square and Triangle classes.