Psuedo-classical Inheritence in JavaScript

Yesterday I wrote about how to perform pseudo-classical inheritance and I wanted to follow up on that post with a few key distinctions. This is the example I gave of how to perform pseudo-classical inheritance:

function Fruit(sweetness, freshness, organic) {
  this.sweetness = sweetness;
  this.freshness = freshness;
  this.organic = organic;
}

function Apple(sweetness, freshness, organic) {
  Fruit.call(this, sweetness, freshness, organic);
  this.color = "red";
  this.name = "apple";
}

Apple.prototype = Object.create(Fruit.prototype);
Apple.prototype.constructor = Apple

In this example it appears as though there are two distinct lines of code of where inheritance is occurring. Lines Fruit.call(this, sweetness, freshness, organic); and Apple.prototype = Object.create(Fruit.prototype);. Both of these lines of code are involved in pseudo-classical inheritance, but do you know what each one does?

Calling SuperClass Constructor

Fruit.call(this, sweetness, freshness, organic); is actually has no role in establishing a delegation relationship at all. This line does not really have anything to do with inheritance per se. What this line really does is call the the super classes constructor in the context of a child. Conceptually it does the same thing that super does in Ruby or Python.

Establishing the Delegation Relationship

Apple.prototype = Object.create(Fruit.prototype); is the line of code solely responsible for establishing the prototypal chain. In my previous article I was more focused on this relationship so I will not write about it much here. I just wanted to take this time to focus on the distinction between calling the super class constructor and establishing the delegation relationship.