Awaiting results of a promise array that's being populated

Question

I'd like to be able to start execution of an array of Promises with Promise.all or Promise.map (Bluebird), while that array is still being populated and then await the results when done populating the array. This is useful when dealing with large datasets that take a long time to load or could cause memory constraints.

Example of how it works today, using a mongodb cursor to load data (using bluebird's Promise.map):

// This is a time-intensive operation
// and requires loading all values into
// memory before proceeding
const dataArray = await cursor.toArray();

// Start doing work after all objects are in memory
await Promise.map(dataArray, doSomeWork);

// done

Example of how I'd like it to work:

const dataArray = [];
const minItems = N;
let promiseMap = null;

// Populate the data array one item at a time
while (await cursor.hasNext()) {
  dataArray.push(await cursor.next());
  if (!promiseMap && dataArray.length > minItems) {
      // Start doing work once there is some data to
      // work with and keep filling the array
      promiseMap = Promise.map(dataArray, doSomeWork);
  }
}

// Once done filling the array, wait for all promises to resolve
await promiseMap;

// done

Is this possible or is it a hard requirement to have a static array of promises before proceeding with execution?

Answer 1

From the docs it looks like eachAsynch can handle a promise returned by the doSomeWork function, waiting for it to finish before continuing...

var cursor = someQuery.cursor();
cursor.eachAsync(doc => doSomeWork(doc)).then(result =>
    /* after all docs processed */);