Nested Async javascript functions

Question

I am using waterline + sails for one api and i have the following function that has nested exec() calls.

AcademyService.getAll().exec(function (error, data) {

        if (error) {

            return res.json({result: false, message: error});

        }

        var academies = data;

        for (var i = 0; i < Object.keys(academies).length; i++) {

            var user_id;

            user_id = academies[i].academy_user_id;

            (function (index) {

                UserService.getOneById(user_id).exec(function (error, data) {

                    if (error) {

                        academies[index].academy_user_id = null;

                    }

                    academies[index].academy_user_id = data.user_fname+" "+data.user_lname;

                });

            })(i);

        }

        return res.json({result: true, academies: academies});

    });

Problem with above code is that, the last return statement does not have updated academies object. i.e. it does not have the updated value for its academy_user_id. I attribute this to the asynchronous behaviour of the calls and i think the when we reach the last return, the async calls for UserService are still running in the loop and updated academies object is not passed on.

Now, a hasty solution is to return the academies object from within the UserService.getOneById callback with a loop end check but that does not seem to be the right approach. So,can we somehow do the inner exec() synchronously?

a cool solution would be to use promises: developer.mozilla.org/en/docs/Web/JavaScript/Reference/… — Meiko Rachimow
– Meiko Rachimow, Commented Mar 8, 2016 at 8:57

elssar · Accepted Answer · 2016-03-08 09:44:33Z

1

Sails comes bundled with the async library, which is ideal for such a situation. Async is available globally in sails, so you don't need to require it, or even add it to your dependencies.

Use async.each instead of your for loop.

Something like this should work

AcademyService.getAll().exec(function(error, academies) {
    if (error) {
        return res.json({
            result: false,
            message: error
        });
    }

    async.each(
        academies,
        function (academy, cb) {
            var user_id = academy.user_id;

            UserService.getOneById(user_id).exec(function (err, user) {
                if (err) {
                    academy.academy_user_id = null;
                }
                else {
                    academy.academy_user_id = user.user_fname + ' ' + user.user_lname;
                }

                return cb();
            });
        },
        function (err) {
            if (err) {
                return res.json({
                    result: false,
                    message: err
                });
            }

            return res.json({
                result: true,
                academies: academies
            });
        }
    );
});

answered Mar 8, 2016 at 9:44

elssar

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1 Comment

xmaestro Over a year ago

Wow. I wanna know where you live :D Just the solution i wanted. Thanks!

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