Synchronous database retrieve javascript

Question

I'm new to javascript and I'm strugguling with synchonous/asynchronous function call, especially here, as i'm trying to concatenate data from two collections of the same database.

Here is my code:

function getAcquisitionAreas(req) {
  PartAreas.getAcquisitionAreasByAcquisitionId(req.params.id, (err, partArea) => {
    particle.areas = partArea._doc.areas;
  });
}

function getAcquisitionPerimeters(req) {
  PartPerimeters.getAcquisitionPerimetersByAcuiqisiontId(req.params.id, (err, partPerimeter) => {
    particle.borders_intern = partPerimeter._doc.borders_intern;
    particle.borders_extern = partPerimeter._doc.borders_extern;
  });

}

function getParticleData(req, callback) {
  getAcquisitionAreas(req);
  getAcquisitionPerimeters(req);
  callback;
}

function constructParticle(req) {
  particle.id = req.params.id;
}

// Register
router.get('/get/:id', (req, res, next) => {
  getParticleData(req);
  constructParticle(req);
  res.send(particle);
});

and it returns {"id":"1508515120"}, this means it execute res.send(particle) before putting in areas and borders. How should I implement this? I've seen Promises but couldn't make it work, and implementing callback methods in callback methods seems very dirty.

Thanks!

Edit

var particle;

function getAcquisitionAreas(req) {
    return new Promise((resolve, reject) => {
    PartAreas.getAcquisitionAreasByAcquisitionId(req.params.id, (err, partArea) => {
            if (err) { reject(err); }

        particle.areas = partArea._doc.areas;
        resolve();
    });
});
}

function getAcquisitionPerimeters(req) {
    return new Promise((resolve, reject) => {
    PartPerimeters.getAcquisitionPerimetersByAcuiqisiontId(req.params.id, (err, partPerimeter) => {
        if (err) { reject(err); }

        particle.borders_intern = partPerimeter._doc.borders_intern;
        particle.borders_extern = partPerimeter._doc.borders_extern;
        resolve();

    });
   })
}

function constructParticle(req) {
    return new Promise((resolve, reject) => {
    particle.id = req.params.id;
        resolve();
    })
}

function sendParticle(res) {
    res.send(particle);
}

// Register
router.get('/get/:id', (req, res, next) => {
    particle = {};
    getAcquisitionAreas(req)
        .then(getAcquisitionPerimeters(req))
        .then(constructParticle(req))
        .then(sendParticle(res));
});

Edit 2

I finally managed to have a working solution:

function getAcquisitionAreas(particle) {
    return new Promise((resolve, reject) => {
    PartAreas.getAcquisitionAreasByAcquisitionId(particle.id, (err, partArea) => {
            if (err) { reject(err); }

        particle.areas = partArea._doc.areas;
        resolve(particle);
    });
});
}

function getAcquisitionPerimeters(particle) {
    return new Promise((resolve, reject) => {
    PartPerimeters.getAcquisitionPerimetersByAcuiqisiontId(particle.id, (err, partPerimeter) => {
        if (err) { reject(err); }
        else {        
            particle.borders_intern = partPerimeter._doc.borders_intern;
            particle.borders_extern = partPerimeter._doc.borders_extern;
            resolve(particle);
        }
    });
   })
}



// Register
router.get('/get/:id', (req, res, next) => {
    particle = {"id":req.params.id};
    getAcquisitionAreas(particle)
        .then(getAcquisitionPerimeters)
        .then((particle) => {res.send(particle)});
});

Answer 1

There are several ways of achieving this(Promises, Yield, Async/Await). You've tried Promises, so let's go through that. I've made some assumptions here, and there are neater ways of doing it, but given what you posted the code sample below should get you most if not all the way there I think.

function getAcquisitionAreas(req) {
    return new Promise((resolve, reject) => {
    PartAreas.getAcquisitionAreasByAcquisitionId(req.params.id, (err, partArea) => {
            if (err) { return reject(err); }

        particle.areas = partArea._doc.areas;
        resolve();
    });
});
}

function getAcquisitionPerimeters(req) {
    return new Promise((resolve, reject) => {
    PartPerimeters.getAcquisitionPerimetersByAcuiqisiontId(req.params.id, (err, partPerimeter) => {
            if (err) { return reject(err); }
        particle.borders_intern = partPerimeter._doc.borders_intern;
        particle.borders_extern = partPerimeter._doc.borders_extern;
        resolve();
        });
   })
}

function getParticleData(req, callback) {
    getAcquisitionAreas(req)
        .then(getAcquisitionPerimeters(req));
        .then(callback);
}

function constructParticle(req) {
    particle.id = req.params.id;
}

// Register
router.get('/get/:id', (req, res, next) => {
    getParticleData(req, () => {
        constructParticle(req);
            res.send(particle);
    });
});

I'm not doing things like catching the errors thrown when the promises are rejected, and to me it seems strange to switch from promises to a callback in the middle, but hopefully the example above will give you a basic idea of how to use them.