http-server-listen.js

async function listenRepeatedly(entity: string, server: Server, port: number) {
  for (let i=0; i<10; i++) {
    const currentPort = port + i;
    try {
      await listenOnce(server, currentPort);
      console.log(`${entity}: listening at port ${currentPort}.`);
      return;
    } catch (err) {
      if (err.code === 'EADDRINUSE') {
        console.log(`${entity}: port ${currentPort} in use, trying next port...`);
        server.close();
      } else {
        throw err;
      }
    }
  }
}

function listenOnce(server: Server, port: number) {
  return new Promise((resolve, reject) => {
    const listeningListener = () => {
      server.removeListener('error', errorListener);
      resolve();
    };
    const errorListener = (err: NodeJS.ErrnoException) => {
      server.removeListener('listening', listeningListener);
      reject(err);
    };
    server.once('listening', listeningListener);
    server.once('error', errorListener);
    server.listen(port);
  });
}