Is this a correct example of Javascript inheritance?

Question

I am studying ways to apply Object Orientation in Javascript. I found a solution to utilize inheritance. I wonder if there are better ways and how to encapsulate my classes.

What I’ve been doing:

People = function(name){
 this.name = name
 this.age = null; 
};

Employee = function(name){
 People.call(this,name);
 this.IdentificationCode = null;
 this.salary = null;
}

Jonh = new Employee("Jonh Smith");
Jonh.age = 25;
Jonh.IdentificationCode = 35632;
Jonh.salary = 3500;

Answer 1

What you are doing is not exactly inheritance, for nothing in your object John is actually inherited. Javascript heritage is given by means of an internal reference called prototype, that all objects possess. It points to another object, and all properties and methods of the prototype are inherited by the object containing the reference. In the case of Javascript, this is particularly useful for methods.

One of the ways to assign yourself prototype an object is to define the property prototype of a function, and then invoke it as a manufacturer using the operator new. The instantiated object will have as prototype the object defined as .prototype of the constructor. For example:

// Define "classe" Pessoa
function Pessoa(nome, idade) {
    this.nome = nome;
    this.idade = idade;
}

// Toda pessoa tem uma método fazAniversário
Pessoa.prototype.fazAniversario = function() {
    this.idade++;
}

// Define classe Funcionario
function Funcionario(nome, idade) {
    Pessoa.call(this, nome, idade);
    this.salario = null;
}

// Todo funcionário herda de Pessoa
Funcionario.prototype = Object.create(Pessoa.prototype);

// Teste
var joao = new Funcionario('João', 25);
joao.fazAniversario();
alert(joao.idade); // 26

The line of Object.create is what makes the inheritance. Object.create receives one object and returns another whose prototype is the object passed. In the above code, this returned object is used as a prototype for all instances of Funcionario, who therefore inherit the method fazAniversario. It is worth pointing out that the Object.create not supported in older browsers like IE8. The link above contains a polyfill which can be used for these browsers to partially support this method.