Non-Instance Safe JS

instance-pollution.js

function Cat(colour, size) {
  this.colour = colour;
  this.size = size;

}

Cat.prototype.meow = function() {
  console.log("Meow");
};

function Garfield() {
}

Garfield.prototype = new Cat('orange', 'fat');

var gf = new Garfield();

gf.meow(); //Meow, as expected.

Cat.prototype.swish = function() {
  console.log("TAIL SWISH!");
};

gf.swish(); //TAIL SWISH, even though it wasn't part of the original inheritance. 

pardon me if I interrupt something... but I feel you are as confused as I was, a month ago. It seems like you want Garfield to stop inheriting Cat's functions after creating Garfield "class".

The book "Programming JavaScript Applications" by Eric Elliot (O'reilly), says that object composition is better than class inheritance. Give this a look! https://gist.github.com/VengadoraVG/6673196e840102c7874a

I recommend you that book... it is really good! read the Chapter 3: Objects, by the time you get to "The Flightweight Pattern", I think you'll understand javascript's inheritance better :)

I hope it helps!

@VengadoraVG: Thanks for the comment, however this particular Gist was used as part of a blog post to demonstrate precisely Elliot's technique. Please see: http://www.donburks.com/mixin-up-your-objects/