Let's finish off this chapter with a more practical example of using inheritance. The task is to be able to calculate the area and the perimeter of different shapes, as well as to draw them, while reusing as much code as possible.

Let's have one `Shape`

constructor that contains all of the common parts. From there, let's have `Triangle`

, `Rectangle`

, and `Square`

constructors, all inheriting from `Shape`

. A square is really a rectangle with the same-length sides, so let's reuse `Rectangle`

when building the `Square`

.

In order to define a shape, you'll need points with `x`

and `y`

coordinates. A generic shape can have any number of points. A triangle is defined with three points, a rectangle (to keep it simpler)—with one point and ...

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