Inside async function, returning value from a callback function returns Promise(undefined) [duplicate]

Question

I'm new to asynchronous programming, I'm facing issue similar to this question, in this question suggested approach uses callbacks but I'm trying to do it using Promises and async-await functions. I get undefined in the console. Here's my example. what am I missing?

 //Defining the function
 async query( sql, args ) {
    const rows = this.connection.query( sql, args, async( err, rows ) => 
     { 
        if ( err )
           throw new Error(err); 
        return rows; 
      } );
}

//calling the function here 
 db.query("select 1")
 .then((row) => console.log("Rows",row)) // Rows undefined
 .catch((e) => console.log(e));

You don't put async on a callback function. You use the Promise constructor, and then you use await instead of then when you're calling the function. — Bergi
– Bergi, Commented Jan 30, 2018 at 15:04

Bergi · Accepted Answer · 2018-01-30 15:05:03Z

7

make your query function return a Promise

function query(sql, args) {
    return new Promise(function (resolve , reject) {
        this.connection.query(sql, args, (err, rows) => {
            if (err)
                reject(err);
            else
                resolve(rows)
        });
    });
}


//calling the function here 
query("select 1")
.then((row) => console.log("Rows",row)) // Rows undefined
.catch((e) => console.log(e));

edited Jan 30, 2018 at 15:05

Bergi

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answered Jan 30, 2018 at 14:58

Ali Faris

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2 Comments

Maryam Dairkee Over a year ago

This works, but can't we do it using async and await in query function?

Aaron Tribou Over a year ago

If you really wanted to use async/await inside the outside query function, you could "await new Promise(...)". Regardless, you still need a Promise to convert the callback whether you use async/await or just plain Promises.

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