Uncaught TypeError: e[n] is not a function

[Cuenca]

return (0, s.default)(e, [{
  key: "_notify",
  value: function value(e, t) {
    var n = void 0,
        r = e.length;

    for (n = 0; n < r; n++) {
      e[n](t);
    }
  }
}...

e[n] can be undefined sometimes