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

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.