CODEWITHSUNDEEP
javascriptnode.jsasynchronousasync-await
drhanlau
drhanlau

Reputation: 2527

Properly terminate NodeJS Async Await

I wrote the following code to connect to MongoDB wrapped in a Promise, but as soon as it is connected, my NodeJS code is still running / not exit properly. May I know what is the proper way to return or terminate it? 

function connectDB() {
  return new Promise (resolve => {
    MongoClient.connect(mongoUrl, function( err, db ) {
      _db = db;
      resolve(db);
    });
  })
}


(async function crawl() {
  const db = await connectDB(); 
  console.log('You are connected');
})()

Upvotes: 1

Views: 3508

Answers (2)

Bergi
Bergi

Reputation: 665090

This isn't really related to async/await, it also happens without. As @Torazaburo stated in the comments, the db driver maintains an open connection to the database, and this open socket (along with its eventhandlers) prevents node from quitting. Closing the connection helps:

function connectDB() {
  return new Promise (resolve => {
    MongoClient.connect(mongoUrl, function(err, db) {
      if (err) reject(err);
      else resolve(db);
    });
  });
}

(async function crawl() {
  const db = await connectDB(); 
  console.log('You are connected');
  db.close();
  console.log('You are no longer connected. Bye!');
})()

Upvotes: 4

Florian35
Florian35

Reputation: 1

A promise have 2 paramaters: resolve and reject.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise

You need to change your promise declaration:

return new Promise ((resolve, reject) => {
  // ...
}

After that, add return statement to your promise:

return resolve(db)

Also, i suggest you to add an error log to your promise:

if (err) return reject(err)

And catch this error.

Good luck!

Upvotes: -2

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