A toggleable object.

toggleable.js

var Toggleable = function(a, b) {
  this._a = a;
  this._b = b;
};

Toggleable.prototype.valueOf = function() { return this._a; };


Toggleable.prototype.toggle = function() {
  if (this.valueOf() == this._a) {
    this.valueOf = function() { return this._b; };
  } else {
    this.valueOf = function() { return this._a; };
  }
};

var foo = new Toggleable(1, 2);
foo + foo;
// 2
foo.toggle();
// 4