CODEWITHSUNDEEP
javascriptnode.js
jedu
jedu

Reputation: 1331

Async await promise pending

I am trying to create a function that adds and returns the next highest value from a mysql table row based on a search criteria. My function looks like:

    async function getNextNumber(systemType){
        let newCounter
        try{
            if(systemType == 'POS'){
                await pool.query(`Update counters set value = value + 1 where type = 'POS'`)
                let newCounter == await pool.query(`Select value from counters where type = 'POS'`)
                console.log(newCounter)
            }

            if(systemType == 'ST'){
                await pool.query(`Update counters set value = value + 1 where type = 'ST'`)
                let newCounter = await pool.query(`Select value from counters where type = 'ST'`)
            }



            return newCounter
        }
        catch(err){
            console.log(err)
        }


    }



console.log(getNextNumber('POS'))

This gives me:

Promise { pending}

[ RowDataPacket { value: 101 } ]

I wanted the [ RowDataPacket { value: 101 } ] result where it says promise pending.

I also tried:

async function test(){
    console.log(await getNextNumber('QC'))
}

This gives me no result

Upvotes: 0

Views: 2026

Answers (1)

jfriend00
jfriend00

Reputation: 707148

I see several coding errors:

  1. Only your first declaration of let newCounter should have the let in front of it. When you then assign newCounter a value, remove the let. That is creating a new locally scoped (to the local block) variable, assigning a value to it and then it goes out of scope and the top level newCounter never gets a value.

  2. Assignment is done with =, not with == unless all you want in the variable is a boolean. So change let newCounter == await pool.query(...) to just newCounter == await pool.query(...).

  3. All async functions return a promise and you HAVE to use .then() or await on the returned promise from calling getNextNumber(). So, your second try with console.log(await getNextNumber('QC')) should work once you fix the other coding errors.

And, then one more thing to check.

Are you 100% sure that your version of your database is returning a promise from pool.query()? await ONLY does something useful if the value you are awaiting is a promise and it contains no magic to make other types of asynchronous operations actually wait and return a value. await needs to be used with a promise.

Putting this together (and assuming you're using the right pool.query() interface that returns a promise:

async function getNextNumber(systemType) {
    let newCounter;
    try {
        if (systemType == 'POS') {
            await pool.query(`Update counters set value = value + 1 where type = 'POS'`);
            newCounter = await pool.query(`Select value from counters where type = 'POS'`);
            console.log(newCounter);
        } else if (systemType == 'ST') {
            await pool.query(`Update counters set value = value + 1 where type = 'ST'`);
            newCounter = await pool.query(`Select value from counters where type = 'ST'`);
        } else {
            // probably need some other return value or error handling here
            throw new Error("invalid systemType in getNextNumber()")
        }
        return newCounter;

    } catch (err) {
        console.log(err)
        throw err;            // need to propagate the error
    }

}

console.log(await getNextNumber('POS'));

// or with error handling
getNextNumber('POS').then(val => {
    console.log(val);
}).catch(err => {
    console.log(err);
});

Upvotes: 2

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