const renderHTML = (store, renderProps) => {
	const components = (
		<Provider store={store}> // use redux
			<RouterContext {...renderProps} /> // the main app through `renderProps`, matched components with react router
		</Provider>
	)
    const reactHTML = ReactDOM.renderToString(components)

	return reactHTML
}

const app = new Koa()
... route matching .... (see example above)