Asynchronous Queries in node.js, waiting and promises

Question

I have a hard time being able to chain functions in node.js, i can't get the receiver to wait. Shouldn't promises be asynchronous and therefore suited for such a task?

const promise = new Promise((resolve, reject) => {
  var input = 'SELECT * FROM ideas;';
  connection.query(input, (err, results) => {
    if(err) {
      console.log(err);
      reject();
    } else {
      console.log('success');
      results = JSON.stringify(results);
      console.log(results);
      resolve();
      return results;
    }
  })
});

promise.then(function(results) {
  results = JSON.parse(results);
  console.log(results);
});

I hope someone knows what I am missing here and can help!

FYI, if you install and use require('mysql2/promise');, then you can use built-in promise support with your database rather than manually promisifying each operation. — jfriend00
– jfriend00, Commented Jan 31, 2020 at 15:26

Dharman · Accepted Answer · 2023-01-13 12:55:02Z

1

You only need to add results to resolve and err to reject.

For an example, you can use this code below:

const promise = new Promise((resolve, reject) => {
  var input = 'SELECT * FROM ideas;';
  connection.query(input, (err, results) => {
    if(err) {
      reject(err);
    } else {
      console.log('success');
      results = JSON.stringify(results);
      console.log(results);
      resolve(results);
    }
  })
});

promise.then(function(results) {
  results = JSON.parse(results);
  console.log(results);
}).catch(error => {
  console.log(error);
})

edited Jan 13, 2023 at 12:55

Dharman♦

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answered Jan 31, 2020 at 15:14

Titus Sutio Fanpula

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Comments

Arslan Ansari · Accepted Answer · 2020-01-31 15:27:22Z

0

Send some data back in the reject() or the resolve() statement, Currently you are expecting some results but noting is being sent back. Just convert your Reject and Resolve statement like this: resolve(results); reject(err);

An Extra tip, also chain a catch block with the promise.then call so that exceptions are also handled successfully. as following promise.then(function() { //code if promise resolves }).catch(function(){ //code if promise rejects });

answered Jan 31, 2020 at 15:27

Arslan Ansari

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