Wrong versus right way to do OO in JS

wrong_vs_right_oo_in_js.js

/* Reading https://drboolean.gitbooks.io/mostly-adequate-guide/content/ch1.html
 * I have a differing opinion. Please help in sorting it out.
 */


// Original code : or I think wrong way to to Object Oriented code.

var Flock = function(n) {
  this.seagulls = n;
};

Flock.prototype.conjoin = function(other) {
  this.seagulls += other.seagulls;
  return this;
};

Flock.prototype.breed = function(other) {
  this.seagulls = this.seagulls * other.seagulls;
  return this;
};

var flock_a = new Flock(4);
var flock_b = new Flock(2);
var flock_c = new Flock(0);

var result = flock_a.conjoin(flock_c)
    .breed(flock_b).conjoin(flock_a.breed(flock_b)).seagulls;

console.log(result); // 32

// --------------------------------------------------------------------//

// My code or the way I think to right way to do OOC

var Flock = function(n) {
  this.seagulls = n;
};

Flock.prototype.conjoin = function(other) {
  return new Flock(this.seagulls + other.seagulls);
};

Flock.prototype.breed = function(other) {
  return new Flock(this.seagulls * other.seagulls);
};

var flock_a = new Flock(4);
var flock_b = new Flock(2);
var flock_c = new Flock(0);

var result = flock_a.conjoin(flock_c)
    .breed(flock_b).conjoin(flock_a.breed(flock_b)).seagulls;

console.log(result); //16

I'd have better OO example that really throws light on problems OO solve, and then reason why we need functional way of thinking. Think, if villain in Terminator 2 was weaker, would we have loved the heroic acts that much?

Flock.prototype.conjoin = function(other) {
  return new Flock(this.seagulls + other.seagulls);
};

Flock.prototype.breed = function(other) {
  return new Flock(this.seagulls * other.seagulls);
};

For the incessant optimizer in me.

conjoin and breed are not pure functions. They depend on mutable variable this.seagulls
flock_a.confoin(flock_b) don't always return same result. If value of seagulls in flock_a is changed, then return value will differ.

Check chapter 3 in the book. Author clearly explained this scenario. He recommends you to use Object.freeze.

Yes the problem with Object.freeze is that a) things can get to the Object before it is frozen and b) attempts to modify the frozen object silently succeed, even without changing anything and without generating any error condition/exception or similar.