doesn't Espruino/Bangle.js support getters and setters?

After some (purely syntactical) experiments, I found that getters/setters within IIFEs seem to be the problem. When trying

let Y = {
  _y:0,
  get y () { return this._y }
};
print(Y.y);

(function () {
  let X = {
    _x:0,
    get x () { return this._x }
  };
  print(X.x);
})();

(edited in the right section of the Espruino IDE, then uploaded to my Bangle.js) the Y-based constructs worked as foreseen (and even produced the intended output), but then the X-based stuff failed.

So, IIFEs seem to have their own (inner) capabilities?