Scoping issue with object array in Javascript

Question

I have a function below within the back-end of my application, and the aim is to return all Sensors associated with a specific thingID.

I was approaching this by populating a new array allSensors, however when logged below

console.log(allSensors); res.send(allSensors)

it is an empty array []

I should also note that individual elements of sensor log correctly

I've moved the

console.log(allSensors)

Into the sensor.findOne loop, and it prints out the elements correctly.

existingThing.sensors.forEach(function (element) { Sensor.findOne({_id: element._id}, function (err, sensor) { if(sensor){ // console.log(sensor); allSensors.push(sensor); console.log(allSensors); // this works.... } }) });

Any ideas as to this behaviour? Thanks

//get all sensors associated with thingid app.get('/api/things/:thingid/sensor', function (req, res) { var allSensors = []; Thing.findOne({ thingID: req.params.thingid }, function (err, existingThing) { if (!existingThing) return res.status(409).send({ message: 'Thing doesnt exist' }); if (existingThing.sensors.length < 0) return res.status(409).send({ message: 'No sensors' }); existingThing.sensors.forEach(function (element) { Sensor.findOne({_id: element._id}, function (err, sensor) { if(sensor){ // console.log(sensor); allSensors.push(sensor); } }) }); }) console.log(allSensors); //empty res.send(allSensors); //empty })

that is not a scoping issue, its an async callback issue, there are plenty of posts to check — juvian
– juvian, Commented Apr 11, 2017 at 16:25
Possible duplicate of Why is my variable unaltered after I modify it inside of a function? - Asynchronous code reference — Andreas
– Andreas, Commented Apr 11, 2017 at 16:25
Here, it is not enough to ensure that the forEach completes – you must also make sure each findOne call completes too. You'll probably want the async library for this. — MultiplyByZer0
– MultiplyByZer0, Commented Apr 11, 2017 at 16:26

MultiplyByZer0 · Accepted Answer · 2017-04-11 16:34:25Z

Install the async library. (It's a seriously useful library, and if you do not use it, you will probably have to reinvent it). Then use this code:

async.each(existingThing.sensors, function(element, _cb) { Sensor.findOne({ _id: element._id }, function(err, sensor) { if(sensor) { allSensors.push(sensor); } _cb(); }); }, function() { console.log(allSensors); res.send(allSensors); });

Great thank you, fairly new to JS so keep missing little things like this..

Collectives™ on Stack Overflow

Scoping issue with object array in Javascript

1 Answer 1

1 Comment

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Linked

Related