basic sapper dev task, with HMR

src/cli/utils.ts

@@ -0,0 +1,18 @@
+import * as net from 'net';
+
+export function wait_for_port(port: number, cb: () => void) {
+	const socket = net.createConnection({ port }, () => {
+		cb();
+		socket.destroy();
+	});
+
+	socket.on('error', err => {
+		setTimeout(() => {
+			wait_for_port(port, cb);
+		}, 100);
+	});
+
+	setTimeout(() => {
+		socket.destroy();
+	}, 100);
+}