js-inheritance.js

//////////////////////
//   Constructors   //
//////////////////////

// This is a constructor. When you call 'new Person', it evokes this function and returns an object with whatever properties got assigned to 'this'.
var Person = function(name, age, weight){
  this.name = name
  this.age = age
  this.weight = weight
  this.location = "Earth"  

  // These functions will be passed along when you inherit attributes from this object since they are defined on 'this'.
  this.consume = function(food){
    if(food){
      console.log(this.name+" is no longer hungry.")
    } else {
      console.log(this.name+"'s stomach rumbles furiously.")
    }
  }

  this.greet = function(){
    console.log("Hey, my name is "+this.name)
  }

}

Person.prototype = {
  complain: function(){
    if(this.hasOwnProperty("college")){
      console.log("I have no time for fun!")
    } else {
      console.log("I can't believe that I am "+this.weight+" lbs.")
    }
  }
}

// Can also do Person.prototype.complain = function(){ code }

// Instantiate a new instance of a person. 
var kevin = new Person("Kevin", 25, 155)
// console.log(kevin.complain())
// console.log(kevin instanceof Person)


////////////////////
//   Inheriting   //
////////////////////

// This is a constructor that takes a parent object. (the 'person' argument in this case)
// We expect it to get it's prototype from a 'new Person'. 
function Astronaut(person, college, genetics, location, callback){
  // First argument in call() is context. The rest are the parent (Person) fuction's arguments.

  // Because the constructor is a function, you can use 'bind', 'apply', and 'call' to set the context of 'this'
  // in which the function is executed and attributes on 'this' get assigned. 
  // You could just as easily set 'this' to any other object, but in this case we want
  // it to set the 'this' properties on the 'new Astronaut' as they would be on a 'new Person'.
  Person.call(this, person.name, person.age, person.weight);

  // If you console.log out 'this' right here, you'll see it only has a person's properties on it.
  // console.log(this)

  // Now we set more properties on 'this'. You can reassign values inherited from Person as well
  // and override inherited functions as well. They are just attributes on the object at this point.
  this.profession = "astronaut"
  this.location = location
  this.college = college
  this.genetics = genetics

  // Callback if you need any other actions to happen before construction is finished.
  // Passing 'this' through will allow you to amend the object or call functions on it.
  callback(this)
}

// Set the prototype of the Astronaut contructor to Person.
// This will allow an Astronaut access to the 'complain' function which it does NOT inherit when using Person.call(). 
Astronaut.prototype = new Person

var spaceman = new Astronaut(kevin, true, "Good", "Moon", function(person){
  person.genetics = "Robust"
  // Prototype functions or attributes can be called without explicitly stating 'Object.prototype.functionName'
  // So you can just use Object.function.
  person.complain()
})

console.log(spaceman)