soapbox/app/soapbox/storage/kv_store.ts

import localforage from 'localforage';

interface IKVStore extends LocalForage {
  getItemOrError: (key: string) => Promise<any>,
}

// localForage
// https://localforage.github.io/localForage/#settings-api-config
export const KVStore = localforage.createInstance({
  name: 'soapbox',
  description: 'Soapbox offline data store',
  driver: localforage.INDEXEDDB,
  storeName: 'keyvaluepairs',
}) as IKVStore;

// localForage returns 'null' when a key isn't found.
// In the Redux action flow, we want it to fail harder.
KVStore.getItemOrError = (key: string) => {
  return KVStore.getItem(key).then(value => {
    if (value === null) {
      throw new Error(`KVStore: null value for key ${key}`);
    } else {
      return value;
    }
  });
};

export default KVStore;