How to manipulate a global state outside of a React component using Recoil?

Question

I'm using Recoil, and I'd like to access the store outside a component (get/set), from within a utility function.

More generally, how do people write re-usable functions that manipulate a global state with Recoil? Using Redux, we can dispatch events to the store directly, but I haven't found an alternative with Recoil.

Using hooks is a great developer experience, but it's hard to convert a function defined within a component to an external utility function because hooks can only be used within a component.

Answer 1

I managed to adapt https://github.com/facebookexperimental/Recoil/issues/289#issuecomment-777249693 answer and make it work with the Next.js framework. (see below usage example)

This workaround allows to use the Recoil Root as a kind of global state. It only works well if there is only one RecoilRoot component, though.

// RecoilExternalStatePortal.tsx
import {
  Loadable,
  RecoilState,
  RecoilValue,
  useRecoilCallback,
  useRecoilTransactionObserver_UNSTABLE,
} from 'recoil';

/**
 * Returns a Recoil state value, from anywhere in the app.
 *
 * Can be used outside of the React tree (outside a React component), such as in utility scripts, etc.

 * <RecoilExternalStatePortal> must have been previously loaded in the React tree, or it won't work.
 * Initialized as a dummy function "() => null", it's reference is updated to a proper Recoil state mutator when RecoilExternalStatePortal is loaded.
 *
 * @example const lastCreatedUser = getRecoilExternalLoadable(lastCreatedUserState);
 */
export let getRecoilExternalLoadable: <T>(
  recoilValue: RecoilValue<T>,
) => Loadable<T> = () => null as any;

/**
 * Sets a Recoil state value, from anywhere in the app.
 *
 * Can be used outside of the React tree (outside a React component), such as in utility scripts, etc.
 *
 * <RecoilExternalStatePortal> must have been previously loaded in the React tree, or it won't work.
 * Initialized as a dummy function "() => null", it's reference is updated to a proper Recoil state mutator when RecoilExternalStatePortal is loaded.
 *
 * @example setRecoilExternalState(lastCreatedUserState, newUser)
 */
export let setRecoilExternalState: <T>(
  recoilState: RecoilState<T>,
  valOrUpdater: ((currVal: T) => T) | T,
) => void = () => null as any;

/**
 * Utility component allowing to use the Recoil state outside of a React component.
 *
 * It must be loaded in the _app file, inside the <RecoilRoot> component.
 * Once it's been loaded in the React tree, it allows using setRecoilExternalState and getRecoilExternalLoadable from anywhere in the app.
 *
 * @see https://github.com/facebookexperimental/Recoil/issues/289#issuecomment-777300212
 * @see https://github.com/facebookexperimental/Recoil/issues/289#issuecomment-777305884
 * @see https://recoiljs.org/docs/api-reference/core/Loadable/
 */
export function RecoilExternalStatePortal() {
  // We need to update the getRecoilExternalLoadable every time there's a new snapshot
  // Otherwise we will load old values from when the component was mounted
  useRecoilTransactionObserver_UNSTABLE(({ snapshot }) => {
    getRecoilExternalLoadable = snapshot.getLoadable;
  });

  // We only need to assign setRecoilExternalState once because it's not temporally dependent like "get" is
  useRecoilCallback(({ set }) => {
    setRecoilExternalState = set;

    return async () => {

    };
  })();

  return <></>;
}

Configuration example using the Next.js framework:

// pages/_app.tsx

import {
  NextComponentType,
  NextPageContext,
} from 'next';
import { Router } from 'next/router';
import React from 'react';
import { RecoilRoot } from 'recoil';
import { RecoilExternalStatePortal } from '../components/RecoilExternalStatePortal';

type Props = {
  Component: NextComponentType<NextPageContext>; // Page component, not provided if pageProps.statusCode is 3xx or 4xx
  err?: Error; // Only defined if there was an error
  pageProps: any; // Props forwarded to the Page component
  router?: Router; // Next.js router state
};

/**
 * This file is the entry point for all pages, it initialize all pages.
 *
 * It can be executed server side or browser side.
 *
 * @see https://nextjs.org/docs/advanced-features/custom-app Custom _app
 * @see https://nextjs.org/docs/basic-features/typescript#custom-app TypeScript for _app
 */
const App: React.FunctionComponent<Props> = (props): JSX.Element => {
  const { Component, pageProps} = props;

  return (
      <RecoilRoot>
        <Component {...pageProps} />
        <RecoilExternalStatePortal />
      </RecoilRoot>
  );
};

// Anywhere, e.g: src/utils/user.ts

const createUser = (newUser) => {
  setRecoilExternalState(lastCreatedUserState, newUser)
}