sapper/sapper-dev-client.js

let source;

function check() {
	if (typeof module === 'undefined') return;

	if (module.hot.status() === 'idle') {
		module.hot.check(true).then(modules => {
			console.log(`[SAPPER] applied HMR update`);
		});
	}
}

export function connect(port) {
	if (source || !window.EventSource) return;

	source = new EventSource(`http://${window.location.hostname}:${port}/__sapper__`);

	window.source = source;

	source.onopen = function(event) {
		console.log(`[SAPPER] dev client connected`);
	};

	source.onerror = function(error) {
		console.error(error);
	};

	source.onmessage = function(event) {
		const data = JSON.parse(event.data);
		if (!data) return; // just a heartbeat

		if (data.action === 'reload') {
			window.location.reload();
		}

		if (data.status === 'completed') {
			check();
		}
	};
}