Putting Togther Q Promises

Question

I'm learning about JS promises and have made some progress in my understanding of things, however unsure how to bring it together with

return

and using

Q.all

So say I have a function: (

getParentsForLocation

returns a promise)

    function doBusiness() {



    return Q.all(

    locations.map(function(item, currentIndex) {

         return getParentsForLocation(item.id)

        .then(function(res) {

             return checkParent(res, currentIndex)

          }



        });

    }))

    .then(_.uniq(locations))

  }

Then following this i.e. after that map has gone through all elements in the

locations

array, I want to run something like underscore's

uniq

function:

_.uniq(someArrayIHave);

Do i need to place this in a
Q.all([])
? \

If so, would it run each method in that array sequentially?

I presume there is something I'd need to do with that
doBusiness()
function, e.g. return some promise, but unsure how that would look?

Any help appreciated.

Many Thanks.

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Answer 1

Do i need to place this in a Q.all(…)?

Yes. Your map() call should get you an array of promises.

If so, would it run each method in that array sequentially?

No. Or at least, we don't know, they could do anything on the inside.

I presume there is something I'd need to do with that doBusiness() function, e.g. return some promise

Yes. From my promise rules of thumb: If a function does something asynchronous, it must return a promise. This is also true for your two callback functions.

How would that look?

function doBusiness() {
    return Q.all(locations.map(function(item, currentIndex) {
//  ^^^^^^ ^^^^^^
        return getParentsForLocation(item.id)
//      ^^^^^^
        .then(function(res) {
            return updateDB(res, currentIndex);
//          ^^^^^^
        });
    }));
//    ^
}

Putting Togther Q Promises

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