6. Heritage and prototypes

Javascript is a prototyping language, so it provides objects, but not classes natively. The difference between prototyping and class-based languages lies in the way objects are created. In class-based languages, all objects of the same class have the same structure (the same fields) and the same behavior (methods). In prototype languages, objects are created by cloning. A clone initially acquires all the properties and behaviors of the parent object (in Javascript, this is called a prototype). It can evolve independently of its prototype and dynamically acquire (or lose) new behaviors or properties.

We'll start by presenting prototypes, the concept on which ECMAScript 2015 has built a system of classes associated with new syntaxes for declaring them.

Every object (including table, function, regular expression, etc.) has a prototype that...