JavaScript Shape Class: Calculate area for circle and triangle

JavaScript OOP: Exercise-5 with Solution

Write a JavaScript program that creates a class called 'Shape' with a method to calculate the area. Create two subclasses, 'Circle' and 'Triangle', that inherit from the 'Shape' class and override the area calculation method. Create an instance of the 'Circle' class and calculate its area. Similarly, do the same for the 'Triangle' class.

Sample Solution:

JavaScript Code:

class Shape {
  calculateArea() {
    throw new Error("Method 'calculateArea()' must be overridden in subclasses");

class Circle extends Shape {
  constructor(radius) {
    this.radius = radius;

  calculateArea() {
    return Math.PI * this.radius * this.radius;

class Rectangle extends Shape {
  constructor(width, height) {
    this.width = width;
    this.height = height;

  calculateArea() {
    return this.width * this.height;

// Create an instance of the Circle class
const circle = new Circle(7);
const circleArea = circle.calculateArea();
console.log(`Circle Area: ${circleArea}`);

// Create an instance of the Rectangle class
const rectangle = new Rectangle(8, 9);
const rectangleArea = rectangle.calculateArea();
console.log(`Rectangle Area: ${rectangleArea}`);

Sample Output:

"Circle Area: 153.93804002589985"
"Rectangle Area: 72"

Note: Executed on JS Bin


In the above exercise -

In the code above, the "Shape" class has a "calculateArea()" method that throws an error, indicating that it must be overridden by subclasses. This enforces that Shape subclasses must provide their own implementation of the "calculateArea()" method.

The "Circle" class extends "Shape" and overrides the "calculateArea()" method to calculate the area of a circle based on its radius using the formula Math.PI * radius^2.

The "Rectangle" class also extends "Shape" and provides its own implementation of the calculateArea() method to calculate the area of a rectangle based on its width and height using the formula width * height.

Finally, instances of 'Circle' and 'Rectangle' are created. Their respective "calculateArea()" methods are called to calculate and display the circle and rectangle areas.


Flowchart: Calculate area for circle and triangle.
Flowchart: Calculate area for circle and triangle.

Live Demo:

See the Pen javascript-oop-exercise-5 by w3resource (@w3resource) on CodePen.

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