sapper-template/templates/main.js

import { init } from 'sapper/runtime/app.js';

// `routes` is an array of route objects injected by Sapper
init(document.querySelector('#sapper'), __routes__);

if (__dev__) {
	// Enable hot-module reloading
	import('sapper/webpack/hmr');
	if (module.hot) module.hot.accept();
}