What is the functionality behind object inheritance using the clone() method in this implementation?

Question

What is the functionality behind object inheritance using the clone() method in this implementation?

I am currently exploring kangax's blog post titled Why ECMAScript 5 still does not allow subclassing an array. In this article, he introduces a unique approach to subclassing that deviates from the traditional prototypal method.

BaseClass.prototype = new Superclass();

What he is demonstrating can be summarized as follows:

function clone(obj) {
  function F() { }
  F.prototype = obj;
  return new F();
}

This sets up inheritance like so:

function Child() { }
Child.prototype = clone(Parent.prototype);

Could someone elaborate on this two-step inheritance process and outline the advantages it offers over the more straightforward single line code mentioned above?

Edit: Following the feedback in the comments, I have learned about the standard Object.create() which serves a similar purpose as the clone() method. How does this particular implementation of clone() operate?

javascript

Answer 1

Answer №1

That's a thought-provoking question. The code snippet you've shared (specifically the clone function) was coined as "prototypal inheritance" by Douglas Crockford. He goes into detail about it in this article on his website. This approach gained popularity and eventually became formalized in ECMA script 5 with Object.create(). If you delve into the object create specification, you'll find that it mirrors Crockford's original concept. Here's how it can be utilized:

var Animal = {
    species: "mammal",
    noises: function () {
        console.log("makes noises")
    },
    actions: ["roll back", "jump up"]
}

var Cat = Object.create(Animal);
Cat.name = "blacky"
Cat.miau = function () {
    console.log("miau miau");
}

Crockford often refers to this as differential inheritance, as it involves specifying only the differences between subclass and superclass when adding new properties. For example, Cat has its own unique properties like "name" and method "miau".

A potential downside is that reference values such as arrays are still shared among instances.

For instance:

var Cat2 = Object.create(Animal);
Cat2.actions.push("bite Henry");
Cat2.actions
["roll back", "jump up", "bite Henry"]
Cat.actions
["roll back", "jump up", "bite Henry"]

However, primitive properties of instances are not shared, which is a positive aspect.

Cat2.name
undefined
Cat.name
"blacky"

Answer 2

That's a thought-provoking question. The code snippet you've shared (specifically the clone function) was coined as "prototypal inheritance" by Douglas Crockford. He goes into detail about it in this article on his website. This approach gained popularity and eventually became formalized in ECMA script 5 with Object.create(). If you delve into the object create specification, you'll find that it mirrors Crockford's original concept. Here's how it can be utilized:

var Animal = {
    species: "mammal",
    noises: function () {
        console.log("makes noises")
    },
    actions: ["roll back", "jump up"]
}

var Cat = Object.create(Animal);
Cat.name = "blacky"
Cat.miau = function () {
    console.log("miau miau");
}

Crockford often refers to this as differential inheritance, as it involves specifying only the differences between subclass and superclass when adding new properties. For example, Cat has its own unique properties like "name" and method "miau".

A potential downside is that reference values such as arrays are still shared among instances.

For instance:

var Cat2 = Object.create(Animal);
Cat2.actions.push("bite Henry");
Cat2.actions
["roll back", "jump up", "bite Henry"]
Cat.actions
["roll back", "jump up", "bite Henry"]

However, primitive properties of instances are not shared, which is a positive aspect.

Cat2.name
undefined
Cat.name
"blacky"

Answer 3

Answer №2

Exploring the importance of using Object.create or a helper function to establish prototype for inheritance can be visually illustrated through the code snippet below:

function Hamster(name){
  if(name ===  undefined){
    throw new Exception("Name cannot be undefined");
  }
  this.name=name;
};

function RussionMini=function(name){
  Hamster.apply(this,arguments);
};
RussionMini.prototype=new Hamster();//throws Error

While

RussionMini.prototpe=new Hamster("dummyvalue");

is an option, it may not always suffice especially when a dynamic value needs to be passed post object declaration (e.g., a DOM element). Using a dummy value in such cases can lead to code complexity and susceptibility to breakage during refactoring.

In both scenarios, the prototype.constructor remains uncorrected which results in this.constructor pointing to an incorrect function (a similar issue occurs with Object.create(Parent.prototype);`

For more insights on inheritance, overriding functions, and utilizing prototypes within constructor functions, check out: Prototypical inheritance - writing up

Answer 4

Exploring the importance of using Object.create or a helper function to establish prototype for inheritance can be visually illustrated through the code snippet below:

function Hamster(name){
  if(name ===  undefined){
    throw new Exception("Name cannot be undefined");
  }
  this.name=name;
};

function RussionMini=function(name){
  Hamster.apply(this,arguments);
};
RussionMini.prototype=new Hamster();//throws Error

While

RussionMini.prototpe=new Hamster("dummyvalue");

is an option, it may not always suffice especially when a dynamic value needs to be passed post object declaration (e.g., a DOM element). Using a dummy value in such cases can lead to code complexity and susceptibility to breakage during refactoring.

In both scenarios, the prototype.constructor remains uncorrected which results in this.constructor pointing to an incorrect function (a similar issue occurs with Object.create(Parent.prototype);`

For more insights on inheritance, overriding functions, and utilizing prototypes within constructor functions, check out: Prototypical inheritance - writing up

What is the functionality behind object inheritance using the clone() method in this implementation?

Answer №1

Answer №2

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