Promises : How to return a value from a "then" block of "Promise.all" back to the invoking code?

Question

Consider the following situation :

// The caller 

const returnValueEWGP = await generator.GenerateEightWeeks(
  packageId
);         


// The callee 


GenerateEightWeeks = async packageId => {

   let weekPromises = [];
   // A lot of code , eventually we have array of promises "weekPromises" with data

    await Promise.all(weekPromises)
      .then(success => {

        const numberOfZeros = success.filter(x => {
          return x == 0;
        }).length;
        const numberOfOnes = success.filter(x => {
          return x == 1;
        }).length;

        console.log(
          `Before going back to Leads : Zeros : ${numberOfZeros} , Ones : ${numberOfOnes}`
        );
        return {
          zeros: numberOfZeros,
          ones: numberOfOnes
        };
      })
       .catch(failed => {            
        return {
          zeros: 1,
          ones: 0
        };
      });


}

The problem is that returnValueEWGP is always undefined.

How can I get the data back to the invoking code ?

Don't use `then`. `await` the return value of `Promise.all` then do something with the resulting array there. — Quentin, Jan 12 '20 at 19:31

score 0 · Answer 1 · answered Jan 12 '20 at 19:30

You do not return anything really try,

return await Promise.all(weekPromises)
      .then(success => {

        const numberOfZeros = success.filter(x => {
          return x == 0;
        }).length;
        const numberOfOnes = success.filter(x => {
          return x == 1;
        }).length;

        console.log(
          `Before going back to Leads : Zeros : ${numberOfZeros} , Ones : ${numberOfOnes}`
        );
        return {
          zeros: numberOfZeros,
          ones: numberOfOnes
        };
      })
       .catch(failed => {            
        return {
          zeros: 1,
          ones: 0
        };
      });

score -1 · Answer 2 · answered Jan 12 '20 at 19:31

-1

You need to return a value from GenerateEightWeeks. You're currently returning undefined implicitly after all the promises are resolved.

answered Jan 12 '20 at 19:31

Rowland

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Promises : How to return a value from a "then" block of "Promise.all" back to the invoking code?

2 Answers2