Rocket.Chat/client/lib/appLayout.ts

import { Emitter } from '@rocket.chat/emitter';
import { ComponentProps, createElement, lazy, ReactElement } from 'react';
import { Subscription, Unsubscribe } from 'use-subscription';

const MainLayout = lazy(() => import('../views/root/MainLayout'));

type AppLayoutDescriptor = ReactElement | null;

class AppLayoutSubscription extends Emitter<{ update: void }> implements Subscription<AppLayoutDescriptor> {
	private descriptor: AppLayoutDescriptor = null;

	getCurrentValue = (): AppLayoutDescriptor => this.descriptor;

	subscribe = (callback: () => void): Unsubscribe => this.on('update', callback);

	setCurrentValue(descriptor: AppLayoutDescriptor): void {
		this.descriptor = descriptor;
		this.emit('update');
	}

	renderMainLayout(props: ComponentProps<typeof MainLayout> = {}): void {
		this.setCurrentValue(createElement(MainLayout, props));
	}

	render(element: ReactElement): void {
		this.setCurrentValue(element);
	}
}

export const appLayout = new AppLayoutSubscription();