JavaScript Class Extension Lab: extends

Learning Goals

1. Practice writing JavaScript classes that inherit from other classes

Introduction

In this lab we're going to create a geometry application that allows us to calculate different properties of multiple shapes. We'll be using JavaScript's class keyword to build objects that inherit from its base object.

Practice Writing JavaScript classes That Inherit From Other Classes

1. Define a Polygon class. Polygon will accept an Array of integers as a parameter, which will represent each side of a shape.

• Use the get keyword to make a getter method countSides that counts the number of sides (each index in the array).
• Use the get keyword to make a getter method perimeter that calculates the sum of each side (each index in the array) of the polygon. This method will become accessible to its child classes.

2. Define a Triangle class that inherits from Polygon.

• It will automatically have access to count and perimeter inherited from Polygon.
• Use the get keyword to make a getter method isValid that checks if the given 3 sides for a triangle is valid.

The sum of the lengths of any two sides of a triangle is greater than the length of the third side. If you take the three sides of a triangle and add them in pairs, the sum is greater than (not equal to) the third side. If that is not true, then it is not possible to construct a triangle with the given side lengths.

3. Define a Square class that inherits from Polygon.

• It will automatically have access to count and perimeter inherited from Polygon.
• Use the get keyword to make a getter method isValid that checks if the given 4 sides for a square is valid. A square is valid when the lengths of all sides are equal.
• Use the get keyword to make a getter method area that calculates the area of the square.

Resources

• Understanding Getters