if (!it) {
      // Fallback for engines without symbol support
      if (
        Array.isArray(o) ||
        (it = unsupportedIterableToArray(o)) ||
        (allowArrayLike && o && typeof o.length === "number")
      ) {
        if (it) o = it;
        var i = 0;
        var F = function(){};
        return {
          s: F,
          n: function() {
            if (i >= o.length) return { done: true };
            return { done: false, value: o[i++] };
          },
          e: function(e) { throw e; },
          f: F,
        };
      }

      throw new TypeError("Invalid attempt to iterate non-iterable instance.\nIn order to be iterable, non-array objects must have a [Symbol.iterator]() method.");
    }

    var normalCompletion = true, didErr = false, err;

    return {
      s: function() {
        it = it.call(o);
      },
      n: function() {
        var step = it.next();
        normalCompletion = step.done;
        return step;
      },
      e: function(e) {
        didErr = true;
        err = e;
      },
      f: function() {
        try {
          if (!normalCompletion && it.return != null) it.return();
        } finally {
          if (didErr) throw err;
        }
      }
    };
  }