JavaScript is a class-free, object-oriented language, and as such, it uses prototypal inheritance instead of classical inheritance. This can be puzzling to programmers trained in conventional object-oriented languages like C++ and Java. JavaScript's prototypal inheritance has more expressive power than classical inheritance, as we will see presently.
But first, why do we care about inheritance at all? There are primarily two reasons. The first is type convenience. We want the language system to automatically cast references of similar classes. Little type-safety is obtained from a type system which requires the routine explicit casting of object references. This is of critical importance in strongly-typed languages, but it is irrelevant in loosely-typed languages like JavaScript, where object references never need casting.
The second reason is code reuse. It is very common to have a quantity of objects all implementing exactly the same methods. Classes make it possible to create them all from a single set of definitions. It is also common to have objects that are similar to some other objects, but differing only in the addition or modification of a small number of methods. Classical inheritance is useful for this but prototypal inheritance is even more useful.
To demonstrate this, we will introduce a little sugar which will let us write in a style that resembles a conventional classical language. We will then show useful patterns which are not available in classical languages. Then finally, we will explain the sugar.
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