Basic Prototypes

gistfile1.js

// JavaScript could have had nice, clean, minimal prototypal inheritance, but
// for political reasons this was obscured behind confusing class-like syntax.

// A cleaner prototype implementation would just use two straightforward operators or methods:
// - `extend` creates an new object that inherits from another, optionally specifying
//   properties to be set on the new object.
// - `isa` checks if one object is or inherits from another.

var original = ExtendableObject.extend({
  name: "John",
  age: 22
});

var childA = original.extend({
  name: "Bob"
});

var childB = original.extend({
  name: "Sarah"
});


childA.age === 22;
parent.age = 40;
childA.age === 42;

childA.isa( childA ) === true;
childA.isa( childB ) === false;
childA.isa( original ) === true;
childA.isa( ExtendableObject ) === true;

// Do you now how to implement `extend` and `isa` in JavaScript?

// No?

// Your mind has been filled with classish cruft,
// obscuring the true workings of JavaScript's object model!

var ExtendableObject = {
  extend: function( properties ) {
    var constructor = function(){};
    constructor.prototype = this;
    
    var instance = new constructor;
    
    for (key in properties) {
      instance[key] = properties[key];
    }
    
    return instance;
  },
  isa: function( prototype ) {
    var constructor = function(){};
    constructor.prototype = prototype;
    
    return this === prototype || this instanceof constructor;
  }
};


childA.isa( Object ) === false; // because you don't inherit from the Object constructor...
childA.isa( Object.prototype ) === true; // ...you inherit from its prototype!