Wait for promises inside Promise.all to finish before resolving it

Question

I have a Promise.all that executes asynchronous functions mapped on an array input if it's not null and then resolve data to a previously defined Promise:

Promise.all((inputs || []).map(input => {
  return new Promise((resolve, reject) => {
    someAsyncFunc(input)
    .then(intermediateOutput => {
      someOtherAsyncFunc(intermediateOutput )
      .then(output => {
        return Promise.resolve(output )
      })
      .catch(reason=> {
        return Promise.reject(reason)
      })
    })
    .catch(reason => {
      return Promise.reject(reason);
    })
  })
  .then(outputs => {
    resolve(outputs)
  })
  .catch(reason => {
    reject(reason)
  })
}))

I only get empty outputs before even someAsyncFunc finishes its work. How can make Promise.all wait for the promises inside to finish their asynchronous work ?

Answer 1

See jfriend's comment.

someAsyncFunc and someOtherAsyncFunc are function that properly return a promise with something like return new Promise(/*...*/);

this is useless:

.then(output => {
  return Promise.resolve(output )
})

read the Promise documentation

same

.catch(reason=> {
  return Promise.reject(reason)
})

the Promise is already rejecting, you don't need to catch and reject yourself

to make sure Promises are chainable you need to return the Promise

// ...
return new Promise((resolve, reject) => {
  if(inputs == null)
    resolve([]);
  else {
    Promise.all(inputs.map(input => {
      return someAsyncFunc(input)
        .then(someOtherAsyncFunc)
    }))
      .then(resolve)
      .catch(reject)
  }
});

note I would rather not make the arry for Promise.all inline, it adds visual clutter:

return new Promise((resolve, reject) => {
  if(inputs == null)
    resolve([]);
  else {
    const myPromises = inputs.map(input => {
      return someAsyncFunc(input)
        .then(someOtherAsyncFunc)
    });
    Promise.all(myPromises)
      .then(resolve)
      .catch(reject)
  }
});

it may still fail if you made other mistakes.