Re-implementing Recoil APIs / article gists

core.ts

// @see https://github.com/NoriSte/recoil-apis

/**
 * Register a new Recoil Value idempotently.
 * @private
 */
export const registerRecoilValue = <T>(
  recoilId: string,
  recoilValue: RecoilValue<T>
) => {
  const { key } = recoilValue;
  const recoilStore = getRecoilStore(recoilId);

  // the Recoil values must be registered at runtime because of the Recoil id
  if (recoilStore[key]) {
    return;
  }

  if (isAtom(recoilValue)) {
    recoilStore[key] = {
      type: "atom",
      key,
      default: recoilValue.default,
      value: recoilValue.default,
      subscribers: []
    };
  } else {
    recoilStore[key] = {
      type: "selector",
      key,
      subscribers: []
    };
  }
};

/**
 * Subscribe to all the updates of a Recoil Value.
 * @private
 */
export const subscribeToRecoilValueUpdates = (
  recoilId: string,
  key: string,
  callback: Subscriber
) => {
  const recoilValue = getRecoilStore(recoilId)[key];
  const { subscribers } = recoilValue;

  if (subscribers.includes(callback)) {
    throw new Error("Already subscribed to Recoil Value");
  }

  subscribers.push(callback);

  const unsubscribe = () => {
    subscribers.splice(subscribers.indexOf(callback), 1);
  };

  return unsubscribe;
};