code: function(obj, prop, fn) {
        if(!definePropertySupport) return;
        var value = obj[prop];
        object.defineProperty(obj, prop, {
          'enumerable'  : true,
          'configurable': true,
          'get': function() {
            return value;
          },
          'set': function(to) {
            value = fn.call(obj, prop, value, to);
          }
        });
      }
docs: *
  @method watch(<obj>, <prop>, <fn>)
  @returns Nothing
  @short Watches a property of <obj> and runs <fn> when it changes.
  @extra <fn> is passed three arguments: the property <prop>, the old value, and the new value. The return value of [fn] will be set as the new value. This method is useful for things such as validating or cleaning the value when it is set. Warning: this method WILL NOT work in browsers that don't support %Object.defineProperty%. This notably includes IE 8 and below, and Opera. This is the only method in Sugar that is not fully compatible with all browsers. %watch% is available as an instance method on extended objects.
  @example
  
  Object.watch({ foo: 'bar' }, 'foo', function(prop, oldVal, newVal) {
  // Will be run when the property 'foo' is set on the object.
  });
  Object.extended().watch({ foo: 'bar' }, 'foo', function(prop, oldVal, newVal) {
  // Will be run when the property 'foo' is set on the object.
  });
  
  *