ES5 "Classes": Methods in Function() vs Prototype

README.md

JSFiddle

https://jsfiddle.net/rk7vnp01/

example.js

// Version 1
//   In this version, makeSound will be redeclared for every instance. 
//   Not horrible but can cause more memory utilization than needed.
function Animal(type, name, sound) {
    this.type = type;
    this.name = name;
    this.sound = sound;
    this.makeSound = function() {return "The " + this.type + " named " + this.name + " goes " + this.sound + "!";};
}

// Version 2
//   In this version, makeSound will be only be declared once
function AnimalSkinny(type, name, sound) {
  this.type = type;
  this.name = name;
  this.sound = sound;
}

AnimalSkinny.prototype.makeSound = function() {
   return "The " + this.type + " named " + this.name + " goes " + this.sound + "!";
};


var frogFat = new Animal('frog', 'Conner', 'ribbit');
var frogSkinny = new AnimalSkinny('frog', 'Conner', 'ribbit');

console.log("Emitting frogFat", frogFat);
console.log("frogFat spoke:"+frogFat.makeSound());
console.log("Note how the method is visible and declared to the class instance.");
console.log("\n\n");
console.log("Emitting frogSkinny", frogSkinny);
console.log("frogSkinny spoke:"+frogSkinny.makeSound());
console.log("Note how the method is not declared on the class instance but under the protoObject");