Escape hatches

The bits that let non-React code reach into what the hooks are doing — and the errors you can catch.

Reaching the hooks' instances

The hooks memoise one engine per name for the page. These hand you the same instance, not a new one:

import { getSharedStore, getLeader, DEFAULT_NAME } from 'use-everywhere';

getSharedStore(); // the store behind a bare useSharedState()
getSharedStore('settings'); // …behind useSharedState(k, v, { store: 'settings' })
getSharedStore('settings', 'tab'); // a different scope is a different store
getLeader('feed'); // the Leader behind useLeader({ name: 'feed' })

This is how you write to shared state from outside a component — an event handler in a plain module, a service worker message, a Zustand middleware:

// Nowhere near React. Every tab sees it.
getSharedStore('session').set('loggedIn', false);

DEFAULT_NAME is the string the hooks default to ('use-everywhere'), exported so you can target the same bus without hard-coding it.

defineStore must come first

If a store needs persistence, defineStore has to run before anything creates it — and getSharedStore(name) creates it. Call defineStore at module scope. If it runs too late it throws, rather than quietly handing you back a store that isn't persisted.

Errors

Both are real classes, so instanceof works:

import { WindowClosedError, HandshakeTimeoutError } from 'use-everywhere';

try {
  const receipt = await pay.result;
} catch (err) {
  if (err instanceof WindowClosedError) {
    // The user closed the payment window before finishing.
  }
  if (err instanceof HandshakeTimeoutError) {
    // The opened page never called connectToOpener — wrong URL, or it crashed.
  }
}

useOpenedWindow catches these for you and turns them into render state (status: 'closed-early'), so you only need them if you're driving openWindow by hand.

CID_PARAM

The query-string parameter (ue_cid) that openWindow appends to the child's URL to carry the connection nonce. Exported because the child page may want to strip it before it ends up in analytics or a history entry:

import { CID_PARAM } from 'use-everywhere';

const url = new URL(location.href);
url.searchParams.delete(CID_PARAM);
history.replaceState(null, '', url);

Don't try to forge it. It's one of four things the child validates — origin, envelope brand, nonce, and source window — and none of them are optional. See the security model.

Types worth knowing

Version	[counter, clientId] — see the clock
MessageMeta	{ clientId, kind, self } — who sent it, and whether it was you
Peer	{ id, kind, lastSeen }
PeerKind	'tab' | 'worker' | (string & {}) — open, so you can invent your own
MessageMap	The shape you parameterise channels with
BusWire	The discriminated union of everything on the bus
PersistAdapter	Bring your own storage — see defineStore