Sync State

Syncs elf store state across tabs

The syncState() function gives you the ability to synchronize an elf store state across multiple tabs, windows or iframes using the Broadcast Channel API.

First, you need to install the package via npm:

npm install elf-sync-state

To use it you should call the syncState() function passing the store:

import { createStore, withProps } from '@ngneat/elf';
import { syncState } from 'elf-sync-state';

interface AuthProps {
  user: { id: string } | null;
  token: string | null;
}

const authStore = createStore({ name: 'auth' }, withProps<AuthProps>({ user: null, token: null }));

syncState(authStore);

You can pass an optional Options object as the second parameter, which allows you to configure the following:

• channel: the name of the channel (default is the store name with a @store suffix).
• source: a function that receives the store and returns the data to sync. The default is (store) => store.
• preUpdate: a function to map the event message and extract the data. The default is (event) => event.data.
• runGuard: a function that determines whether the actual implementation should run. The default is () => typeof window?.BroadcastChannel !== 'undefined'.
• requestState: a boolean indicating whether the store should request the current source from other instances. The default is false.

import { syncState } from 'elf-sync-state';
import { authStore } from './auth.store';

syncState(authStore, { channel: 'auth-channel' });

The sync state also returns the BroadcastChannel object created or undefined if the runGuard function returns false.

import { syncState } from 'elf-sync-state';
import { authStore } from './auth.store';

const channel: BroadcastChannel | undefined = syncState(authStore);

Sync a subset of the state

The includeKeys() operator can be used with the source option to sync a subset of the state.

import { includeKeys, syncState } from 'elf-sync-state';
import { authStore } from './auth.store';

syncState(authStore, {
  source: (store) => store.pipe(includeKeys(['user'])),
});

Pre Update interceptor

The preUpdate option can be used to intercept the MessageEvent and modify the data to be synchronized taking into account other properties of the event.

import { includeKeys, syncState } from 'elf-sync-state';
import { authStore } from './auth.store';

syncState(authStore, {
  preUpdate: (event) => {
    console.log(event);
    return event.origin === '' ? undefined : event.data;
  },
});

Request state

If the requestState option is enabled, the store will request the initial state from other available stores on the same channel during startup.

import { syncState } from 'elf-sync-state';
import { authStore } from './auth.store';

syncState(authStore, { requestState: true });

Integration with Elf :mage_woman:

The use of this library has been tested together with other Elf libraries, such as elf-entities, elf-persist-state or elf-state-history. I have also tried to be consistent with their programming style and documentation to help with integration.

Here you can see an example of using all of these in an Angular application. Just open the result in two different tabs to see the library in action.

:warning: There may be a desync due to hot reload