1

How can we return a value from promise rather than console.log? If i change console to return(values[1] - values[0]). And try to do console.log(balance(user)), it prints Promise { <pending> }.

I don't know if i am doing it right or not, what am i trying to do is get balance of user by subtracting all purchases from all Deposit/withdrawals. Doing without promises, it returns value before the DB queries are completed. Any better solution? 

function totalPurchases(user) {
return new Promise(function (resolve, reject) {
    Purchase.getTotalPurchases(user, function (err, tot) {
        if (err) {
            // console.log(err);
            reject(new Error("Error: 1002"));
            // return false;
        }
        else {
            resolve(tot[0].purchases);
        }
    })
})
}
function totalDW(user) {
return new Promise(function (resolve, reject) {
    DepWid.getTotalDepwids(user, function (err, tot) {
        if (err) {
            reject(new Error("Error: 1003"));
        }
        else {
            resolve(tot[0].depWids);
        }
    })
})
}

exports.balance = async (user) => {
let promises = [];
promises[0] = totalPurchases(user);
promises[1] = totalDW(user);

Promise.all(promises)
    .then(function (values) {
        console.log(values[1] - values[0]);
        //Return this rather than console.log
    })
    .catch(function (err) {
        console.log(err);
    })
}
Joe Mutti
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  • Do you want to use promise value without using `then`? Possible duplicate of [How do I return the response from an asynchronous call?](https://stackoverflow.com/questions/14220321/how-do-i-return-the-response-from-an-asynchronous-call) – Estus Flask Oct 14 '18 at 05:50

1 Answers1

2

Since balance is an async function, you can await Promise.all and then later return the result.

function totalPurchases(user) {
    return new Promise(function (resolve, reject) {
        setTimeout(function(){
            resolve(5);
        }, 2000);
    })
}
function totalDW(user) {
    return new Promise(function (resolve, reject) {
        setTimeout(function(){
            resolve(3);
        }, 1000);
    });
}

let balance = async (user) => {
    let promises = [];
    promises[0] = totalPurchases(user);
    promises[1] = totalDW(user);   

    const [deposits, withdrawals] = await Promise.all(promises);
    return deposits - withdrawals;
}

balance().then(r => { //If `balance' is called from an async method you can do await here. Else you need to do `then` like I have done here
    console.log(r); //prints 2
});
Boney
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