Raynos/weakmap-shim create-store.ts

create-store.ts

// Original: https://github.com/Raynos/weakmap-shim create-store

type StoreId = Object;
type Store = (obj: Object) => Object;
type Item = { _storeId: StoreId; valueOf: ItemValueOf; };
type ItemValueOf = (storeId?: StoreId) => Object | Item;

const createStore = (): Store => {
  const storeId: StoreId = {};
  return (obj: Object | Item): Item => {
    const objOrItem = (<ItemValueOf>obj.valueOf)(storeId);
    return isItem(objOrItem, storeId)
      ? objOrItem
      : createItem(objOrItem, storeId);
  };
};

const createItem = (obj: Object, storeId: StoreId): Item => {
  const item = { _storeId: storeId };
  const originalValueOf = obj.valueOf;
  Object.defineProperty(obj, 'valueOf', {
    value(s?: StoreId) {
      return s === storeId ? item : originalValueOf.apply(this, arguments);
    },
    writable: true
  });
  return item;
};

const isItem = (
  objOrItem: Object | Item, storeId: StoreId
): objOrItem is Item => {
  return (<Item>objOrItem)._storeId === storeId;
};

export { createStore };