javascript prototype inheritance, apply, call, Object.create

Readme.md

Prototype inheritance

It can be implemented in multiple ways

• using call and apply functions to change the scope of the this keyword
• using the ECMA5 feature Object.create

examples for

• apply
• call
• mixin

inheritance_factory.js

define(function(){
  
  /** 
  * Emulating how Object.create works. 
  * Is the implementation below equivalent with Object.create?
  * just a test
  */

  // Constructor emulating inheritance
  var Constructor = function (parameterMap, parentObject) {
    for(var key in parameterMap) {
      if(parameterMap.hasOwnProperty(key)) {
        this[key] = parameterMap[key];
      }
    }
    if( typeof parentObject !== 'undefined' ) {
      this.prototype = parentObject;
      for(var fn in parentObject) {
        if(!this.hasOwnProperty(fn)) {
          this[fn] = parentObject[fn];
        }
      }
    }
  }

  var testParent = new Constructor( { 
    'name' : 'parent',
    'parentProperty' : 'test',
    'parentFn' : function () { console.log('parent fn'); }
    });

  describe('The factory (the Constructor)', function() {
    it('can create an object', function() {
      expect(testParent).toBeDefined();
    });
    it('can set up the properties', function() {
      expect(testParent.name).toEqual('parent');
      expect(testParent.parentProperty).toEqual('test');
      expect(testParent.parentFn).toBeDefined();
    });
    it('can create an object without a parent object', function() {
      expect(testParent.prototype).toBeUndefined();
    });
  });


  describe('An instance of a parent created by the constructor', function() {

    var testInstance = new Constructor({ 'name' : 'child1'}, testParent);

    it('has a prototype', function() {
      expect(testInstance.prototype).toBeDefined();
    });

    it('has the prototype same as the parent', function() {
      expect(testInstance.prototype).toEqual(testParent);
    });

    it('can have its own properties', function() {
      expect(testInstance.name).toBeDefined();
    });

    it('has the parents functions', function() {
      expect(testInstance.parentFn).toBeDefined();
    });
    
    it('has the parents properties', function() {
      expect(testInstance.parentProperty).toBeDefined();
    });

  });

  describe('An instance of a parent created by Object.create', function() {
    var testInstance = Object.create(testParent);

    it('has the parents properties', function() {
      expect(testInstance.parentProperty).toBeDefined();
    });

    it('has the parents functions', function() {
      expect(testInstance.parentFn).toBeDefined();
    });
  });
})

mokey_patching_with_apply.js

var originalfoo = someobject.foo;
someobject.foo = function() {
  // Do stuff before calling function
  console.log(arguments);
  // Call the function as it would have been called normally:
  originalfoo.apply(this, arguments);
  // Run stuff after, here.
}

prototype_inheritance_ecma5_ObjectCreate.js

function Animal(name) {
    // Instance properties can be set on each instance of the class
    this.name = name;
}

// Prototype properties are shared across all instances of the class. However, they can still be overwritten on a per-instance basis with the `this` keyword.
Animal.prototype.speak = function() {
    console.log("My name is " + this.name);
};

var animal = new Animal('Monty');
animal.speak(); // My name is Monty

// cat inherited from animal

var cat = Object.create(Animal);
cat.speak();

prototype_inheritance_without_Objectcreate.js

function Animal(name) {
    // Instance properties can be set on each instance of the class
    this.name = name;
}

// Prototype properties are shared across all instances of the class. However, they can still be overwritten on a per-instance basis with the `this` keyword.
Animal.prototype.speak = function() {
    console.log("My name is " + this.name);
};

var animal = new Animal('Monty');
animal.speak(); // My name is Monty

// cat inherited from animal

function Cat(name) {
    Animal.call(this, name);
}

Cat.prototype = new Animal();

var cat = new Cat('Monty');
cat.speak(); // My name is Monty