MongoDB 客户端使用异步/等待连接使 function 卡住

Question

MongoDB client connect seems to work but the function just hangs.

app.js

async function test() {
  console.log('Hello world');
  await new Promise((resolve) => {
    setTimeout(resolve, 50);
  });
  console.log('Bye world');
}
test();

When I run using node app.js on cmd, I get the logs and the shell exits as expected. However, when I run this code ->

async function test() {
  console.log('Hello world');
  await MongoClient.connect(MONGODB_URI);
  console.log('Bye world');
}
test();

and I run again using node app.js. This time also I get both the logs but the process never exits. What is happening here? Am I missing something very obvious?

Answer 1

I did figure out what is happening here.

const client = await MongoClient.connect(URI);

returns a connected client to the database. However, if I don't close the connection to the client, the node process remains hanging. So, the code below works as expected.

const client = await MongoClient.connect(URI);
// Execute some queries
await client.close();

Although it might simply be a mistake of me not reading the MongoDB documentation correctly, I'll share the consequence of this error that I was facing.

I had an AWS lambda function code as below:

module.exports.handler = async (event) => {
  const client = await MongoClient.connect(URI);

  // Do something with the client but forgets to close

  const response = {
    statusCode: 200,
    headers: {
      'Access-Control-Allow-Origin': '*',
      'Access-Control-Allow-Credentials': true,
    },
    body: JSON.stringify({ foo: 'bar' }),
  };

  console.log(response);
  return response;
};

I get the log of the response being printed out but the function will timeout and will not return the response.

I pulled some of my hair as it was my first time working with lambdas and MongoDB so remember folks, close your connection after you're done with them.

Hope this helps someone.