• The piece of code below reproduces the error. The weird part is that if you comment out the line where proto is assigned in one (regardless which) of the two constructors you don't get the error. This does not make sense to me.

    var Collection = function Collection(value) {
      return value;
    var KeyedCollection = /*@__PURE__*/ (function (Collection) {
      function KeyedCollection(value) {
        //return isKeyed(value) ? value : KeyedSeq(value);
      if (Collection) KeyedCollection.__proto__ = Collection;
      KeyedCollection.prototype = Object.create(Collection && Collection.prototype);
      KeyedCollection.prototype.constructor = KeyedCollection;
      return KeyedCollection;
    var IndexedCollection = /*@__PURE__*/ (function (Collection) {
      function IndexedCollection(value) {
        //return isIndexed(value) ? value : IndexedSeq(value);
      if (Collection) IndexedCollection.__proto__ = Collection;
      IndexedCollection.prototype = Object.create(Collection && Collection.prototype);
      IndexedCollection.prototype.constructor = IndexedCollection;
      return IndexedCollection;

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