What is the syntax to using await and async in asynchronous functions using nodejs?

Question

I am trying to create a basic API in nodejs to perform CRUD actions on a database. I do not understand why the result is undefined

exports.getPlaylist = async function (req, res) {
  console.log('Recieved getPlaylist request');
  result = await connection.executeQuery('SELECT * from Users');
  res.status(200).send(result);
  console.log(result); // Logs undefined
};

This is the function that gets called and gets the data from the database:

async executeQuery(query) {
    connection.query(query, function (err, result) {
        if (err) {
            console.log('Error executing query: ' + err);
        }

        console.log(result); // logs correct data
        return result;

    });
}

executeQuery does not return anything

bhspencer
– bhspencer

2020-01-20 14:36:33 +00:00
Commented Jan 20, 2020 at 14:36 — bhspencer
– bhspencer, Commented Jan 20, 2020 at 14:36

Cody Geisler · Accepted Answer · 2020-01-20 14:40:45Z

2

You need to "promisify" your callback. (see require('utils').promisify ) for a shorthand for applying to functions that follow node.js callback style (function(err,result){}).

executeQuery(query) {
    return new Promise((res, rej) => {
        connection.query(query, function (err, result) {
            if (err) {
                console.log('Error executing query: ' + err);
                rej(err)
            } else {
                console.log(result); // logs correct data
                res(result);
            }
        });
    });
}

Now inside an async function you can await executeQuery(query)

answered Jan 20, 2020 at 14:40

Cody Geisler

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Comments

Sohail Ashraf · Accepted Answer · 2020-01-20 14:43:39Z

1

The execute is not a promise base function, you cannot use await on a callback function.

change the execute function to promise base

Example:

 executeQuery(query) {
  return new Promise( (resolve, reject) => {
    connection.query(query, function (err, result) {
      if (err) {
          console.log('Error executing query: ' + err);
          reject('Error executing query: ' + err);
      }

      console.log(result); // logs correct data
      resolve(result);

  });
  });

}

Add try catch in your calling function

exports.getPlaylist = async function (req, res) {
  console.log('Recieved getPlaylist request');
  try{
    result = await connection.executeQuery('SELECT * from Users');
    res.status(200).send(result);
    console.log(result); // Logs undefined
  } catch(error) {
    console.log(error)
  }

};

edited Jan 20, 2020 at 14:43

answered Jan 20, 2020 at 14:42

Sohail Ashraf

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1 Comment

Ajay Dabas Over a year ago

You don't need to add async to executeQuery function. You're already returning a Promise. async just wrap the function into a Promise.

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