6. Legacy and prototypes

JavaScript is a prototype-based language, which means it provides objects but, natively, no classes. The difference between prototype-based languages and class-based languages lies in the mechanism used to create objects. In class-based languages, all objects of the same class have the same structure (the same fields) and the same behaviors (methods). In prototype-based 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 will first present the prototypes, a concept on which ECMAScript 2015 has built a class system associated with new syntaxes for their declaration.

Every object (including tables, functions, regular...