Javascript prototype inheritance

gistfile1.js

// There are several ways to instantiate objects in Javascript and show how the prototype chaining works. 
// I have demonstrated two such ways here


// Prototype inheritance Using Object.create()

house = { rooms: 4, square_foot: 2000 };
// Creates an object house, whose prototype is Object.prototype

house_in_sf = Object.create(house);
// Creates an object house_in_sf, whose prototype is house, and goes up the chain to Object.prototype and then to null 

house_in_sf.square_foot = 800 
  
console.log(house_in_sf.rooms) // returns 4
console.log(house_in_sf.square_foot) // returns 800
console.log(house_in_sf.__proto__) // returns { rooms: 4, square_foot: 2000 }
console.log( house.__proto__) // returns literal {}
   

// constructor + prototype

// In this example we see how prototype is used for inheriting behavior from other objects.

var Media = function() {
  this.hasText = true;
  this.describe = function() {
    if (this.hasText) {
      console.log('Media-text' + this.description);
    }
    else {
      console.log('No text provided for media');
    }
  };
};

var Book = function(title, description) {
  this.title = title;
  this.description = description;
  this.describe = function() {
    if (this.hasText) {
      console.log("Title:" + this.title + ",Description:" + this.description);
    }
  };
};

Book.prototype = new Media();

var VoiceMemo = function(description) {
  this.description = description;
  this.hasText = false;
};
VoiceMemo.prototype = new Media();

var book1 = new Book("Wonder", "A children's novel about a 5th grade boy");
book1.describe() 
// Returns Title: Wonder, Description: A children's novel about a 5th grade boy 

var voiceMemo = new VoiceMemo("Call From JK Rowling")
voiceMemo.describe()
// Returns 'No text provided for media'