Express app.listen 返回 Promise { 服务器 {} }

Question

I have an express server running, I am running into an issue while writing unit tests. I have a startup function that connects to database, then returns a Server with app.listen(). The issue is that if I return app.listen from within an async function, I get a Promise with a server inside of it, I have tried to resolve this promise, wait for this promise, return a server from.then(). I do not want the promise I want the server.

express.ts

import express from 'express';

const app = express();

export { app };

startup.ts

import { app } from './express';
import { sequelize } from './sequelize';

app._startup = (async() => {
  switch (process.env.NODE_ENV) {
    case "production":
      await sequelize.authenticate();
      break;
    case "test":
      await sequelize.sync({ force: true });
      break;
    case "development":
    default:
      await sequelize.sync({ force: false });
      break;
  }
})().then(() => true);

export { app };

server.ts

import { app } from './startup';

// export const server = app.listen(8080); // This works

export const server = (
  async() => {
    await app._startup;
    return app.listen(8080); // This does not work
  }
)();

Because the Server {} is inside a Promise {} my unit tests all fail

console.log(server);
// => Promise { Server { } }

How can I resolve this promise before exporting the server?

Answer 1

You can wait for the function to complete the async task. Since you are defining server as an async function you can use await keyword to wait for it to complete. Implementation is as follows:

import { app } from './startup';

export const server = app.listen(8080);
export const server = await (  // use await to wait
  async() => {
    await app._startup;
    return app.listen(8080); // This does not work
  }
)();

Answer 2

Thanks for your comment @jfriend00

The solution is posted below

const server = createServer(app);

(async() => {
  await app._startup;
})().then(() => server.listen(8080));

export { server };