CODEWITHSUNDEEP
typescript
Eddy
Eddy

Reputation: 35

Use reduce with map and array

I am creating small app so that i learn angular, typescript and so on. I find out about reduce function which i can use to sum fields in array. I am trying to implement it in my app but with no luck so far. I have something like this:

    const sumTest: any = data.grades?.map(async (studentNumber) => {
    const getGrade= await dataSources.getStudenGrade(studentNumber);
    return getGrade.grade
    }).reduce((a: any, b: any) =>{ a + b});

That is clearly wrong because i am getting [ Promise { <'pending'> }, Promise { <'pending'> } ] as result. Can somebody help me with that?

Upvotes: 0

Views: 246

Answers (1)

Stephen Cleary
Stephen Cleary

Reputation: 456507

Your mapping result is an array of promises. That's normal; by mapping each item to a promise, you end up with multiple promises.

If you want to asynchronously wait for all the promises to complete, you would use Promise.all:

const sumTest: any = data.grades?.map(async (studentNumber) => {
  const getGrade= await dataSources.getStudenGrade(studentNumber);
  return getGrade.grade;
});
const values = await Promise.all(sumTest);
values.reduce((a: any, b: any) =>{ a + b});

Upvotes: 1

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