client/state/initial-state.js
function getInitialServerState( initialReducer ) {
	if ( typeof window !== 'object' || ! window.initialReduxState || isSupportSession() ) {
		return null;
	}

	const serverState = deserialize( window.initialReduxState, initialReducer );
	return pick( serverState, Object.keys( window.initialReduxState ) );
}
function getInitialServerState( initialReducer ) {
	if ( typeof window !== 'object' || ! window.initialReduxState || isSupportSession() ) {
		return null;
	}

	const serverState = deserialize( window.initialReduxState, initialReducer );
	return pick( serverState, Object.keys( window.initialReduxState ) );
}
get bootstrapped state from a server-side render