Shape Area in JavaScript

You write an abstract class and the areas of three shapes.

Shape is abstract. It has two abstract methods:

• area() returns the shape's area.
• name() returns the shape's name.

It also has one concrete method, describe(). It returns a text such as Square with area 25. That is the name, then with area, then the area.

Three shapes inherit from Shape:

• Rectangle(width, height) has area width × height.
• Square(side) has area side × side.
• RightTriangle(a, b) has sides a and b that meet at a right angle. Its area is a × b / 2, rounded down.

Their constructors and name() methods are already written. You write each area().

JavaScript has no abstract classes. As in the abstract-classes lesson, Shape's area() and name() throw an error. Each shape overrides them.

For each shape, the harness prints describe() on its own line.

Example 1:

Input: new Rectangle(3, 4), new Square(5), new RightTriangle(3, 4)
Output:
Rectangle with area 12
Square with area 25
Right triangle with area 6

Explanation: 3 × 4 = 12 and 5 × 5 = 25.
The triangle is half of 3 × 4, so 6.

Example 2:

Input: new RightTriangle(3, 5), new Square(1)
Output:
Right triangle with area 7
Square with area 1

Explanation: Half of 3 × 5 is 7.5.
It rounds down to 7.

Example 3:

Input: new Rectangle(1, 7), new RightTriangle(1, 1)
Output:
Rectangle with area 7
Right triangle with area 0

Explanation: A 1 by 7 rectangle has area 7.
Half of 1 × 1 rounds down to 0.

Constraints:

• 1 to 100 shapes.
• Each size is a whole number from 1 to 10,000.