How to do promise.all for array of array of promises?

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You need to also call Promise.all for each array item:

const promise4all = Promise.all(
   promiseArray.map(function(innerPromiseArray) {
        return Promise.all(innerPromiseArray);
   })
);

Or directly:

// Fix: Promise.all.bind is required because it seems like Promise.all
// implementation relies on "this"
const promise4All = Promise.all(promiseArray.map(Promise.all.bind(Promise)))
// or
// const promise4All = Promise.all(promiseArray.map(p => Promise.all(p)))

This way the outer Promise.all gets the grouped promises in other Promise.all:

promise4all.then(function(promiseGroupResult) {
  // promiseGroupResult is the actual result of each promise group
  // and you'll be able to get each result this way: promiseGroupResult.somePropertyName
});

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