Question

Reading ‘Javascript The good Parts’ from Crocksford, I’ve been in a quest to write some efficient, readable and reusable JavaScript code.
That’s all I aim, and particularly like the Object’s properties being public.

That being said, is there any particular problem or point of improvement to this code?

( function(){

    window.App = {}

    // define uma pessoa normal
    App.Person = function(name){
        this.name = name || "anon"
        this.iq = 100
        this.fortune_number = Math.floor(Math.random()*100)
    }

    App.Person.prototype.sayName = function() {
        return (this.name+"!")
    }

    App.Person.prototype.sayIQ = function() {
        return (this.iq)
    }



    // define um genio da humanidade
    App.Genius = function(name) {
        App.Person.call( this, name )
        this.iq = 9000
    };
    // inherits All methods from Pessoa
    App.Genius.prototype = App.Person.prototype

    App.Genius.prototype.solveNP = function() {
        return "eureka!"
    };

})()


var p = new App.Person('Jon')
console.log( "A Person:", p.sayName(), p.fortune_number, p.sayIQ() )
//-> A Person: Jon! 10 100

var g = new App.Genius( 'Eugenios' )
console.log( "A Genious:", g.sayName(), g.fortune_number, g.sayIQ(), g.solveNP() )
//-> A Genious: Eugenios! 7 9000 eureka!

I’m particularly unsure if this line App.Genius.prototype = App.Person.prototype is good, because I usually see prototyping after some new instance, like in Mozilla Guide

Answer 1

There is no true inheritance in your code. You HAVE TO extend the prototype chain in order to have true (prototypal) inheritance.

// This is how it's done in JS
Child.prototype = new Parent();
Child.prototype.constructor = Child;

This has the side-effect of executing the Parent constructor which can be bad in some cases (for instance if the constructor expects any parameters). You should use the following bit to do the inheritance.

var Fn = function () {}; // empty constructor, no side-effects
Fn.prototype = Parent.prototype;

Child.prototype = new Fn();
Child.prototype.constructor = Child;