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0

When querying an observable within a forEach loop, does a new "instance" of the observable get created on every loop or does the existing observable get overwritten if the next loop query is requested before the previous observable returns a value?

For example, if I have messages to send to my users, I need to query for all their devices and send to all devices. An example of a topic in the topics array that is passed to createTopics(topics) would be:

Single Item in Topics Array

 "submission": 
 "id": 52,
 "artistID": 111,
 "title": "Sego Sucks",
 "Artist": 
 "name": "Sego"
 
 ,
 "users": [
 
 "id": 7,
 "userUID": "ZvOBNBqxbgRYoibSYEwkL9YKtWG2"
 
 ]
 

My question is, when I run the forEach loop, I have an observable in findUserDevices that is iterated over several times really quickly, will my observable be "overwritten" by the next loop if it doesn't return a value before the next loop comes about? So far when I run this code, it executes as planned, but I am not sure if this is the best way to handle the observable as my data scales and there are more users per topic especially since pushToDevices() is an async function.

function createTopics(topics) 
 topics.forEach((topic: any) => 
 const message = 
 notification: 
 title: `New music from $topic.submission.Artist.name!`,
 body: `Listen to "$topic.submission.title" now`
 
 

 topic.users.forEach((user) => 
 findUserDevices(user.userUID, message);
 )
 )


function findUserDevices(uid: string, message) 
 collectionData(fb.firestore().collection('devices').where('userId', '==', uid)).subscribe((devices: any) => 
 var userDeviceTokens: string[] = devices.map((device: any) => device.token);
 if (userDeviceTokens.length != 0) 
 message['tokens'] = userDeviceTokens;
 pushToDevices(message);
 
 )


async function pushToDevices(message) 
 await admin.messaging().sendMulticast(message).then((response) => 
 console.log('done!')
 )

Thanks for any insight!

javascript typescript rxjs

share|improve this question

asked Mar 25 at 17:56

Jordan LewallenJordan Lewallen

54244 silver badges1212 bronze badges

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  this will just fire off a bunch of async calls
  
  – Rafael
  Mar 25 at 17:59
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  "Does a new instance of the observable get created on every loop?", the answer to that question is yes. This means that you can safely instantiate a new Observable for each iteration of your loop like you are doing here, there is nothing wrong with doing that. It will not overwrite the observable in the previous loop.
  
  – SnorreDan
  Mar 25 at 18:26
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Excellent thank you very much for the clarification both of you!
  
  – Jordan Lewallen
  Mar 25 at 18:40
  

  
  
  
  

add a comment | 

0

When querying an observable within a forEach loop, does a new "instance" of the observable get created on every loop or does the existing observable get overwritten if the next loop query is requested before the previous observable returns a value?

For example, if I have messages to send to my users, I need to query for all their devices and send to all devices. An example of a topic in the topics array that is passed to createTopics(topics) would be:

Single Item in Topics Array

 "submission": 
 "id": 52,
 "artistID": 111,
 "title": "Sego Sucks",
 "Artist": 
 "name": "Sego"
 
 ,
 "users": [
 
 "id": 7,
 "userUID": "ZvOBNBqxbgRYoibSYEwkL9YKtWG2"
 
 ]
 

My question is, when I run the forEach loop, I have an observable in findUserDevices that is iterated over several times really quickly, will my observable be "overwritten" by the next loop if it doesn't return a value before the next loop comes about? So far when I run this code, it executes as planned, but I am not sure if this is the best way to handle the observable as my data scales and there are more users per topic especially since pushToDevices() is an async function.

function createTopics(topics) 
 topics.forEach((topic: any) => 
 const message = 
 notification: 
 title: `New music from $topic.submission.Artist.name!`,
 body: `Listen to "$topic.submission.title" now`
 
 

 topic.users.forEach((user) => 
 findUserDevices(user.userUID, message);
 )
 )


function findUserDevices(uid: string, message) 
 collectionData(fb.firestore().collection('devices').where('userId', '==', uid)).subscribe((devices: any) => 
 var userDeviceTokens: string[] = devices.map((device: any) => device.token);
 if (userDeviceTokens.length != 0) 
 message['tokens'] = userDeviceTokens;
 pushToDevices(message);
 
 )


async function pushToDevices(message) 
 await admin.messaging().sendMulticast(message).then((response) => 
 console.log('done!')
 )

Thanks for any insight!

javascript typescript rxjs

share|improve this question

asked Mar 25 at 17:56

Jordan LewallenJordan Lewallen

54244 silver badges1212 bronze badges

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  this will just fire off a bunch of async calls
  
  – Rafael
  Mar 25 at 17:59
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  "Does a new instance of the observable get created on every loop?", the answer to that question is yes. This means that you can safely instantiate a new Observable for each iteration of your loop like you are doing here, there is nothing wrong with doing that. It will not overwrite the observable in the previous loop.
  
  – SnorreDan
  Mar 25 at 18:26
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Excellent thank you very much for the clarification both of you!
  
  – Jordan Lewallen
  Mar 25 at 18:40
  

  
  
  
  

add a comment | 

When querying an observable within a forEach loop, does a new "instance" of the observable get created on every loop or does the existing observable get overwritten if the next loop query is requested before the previous observable returns a value?

For example, if I have messages to send to my users, I need to query for all their devices and send to all devices. An example of a topic in the topics array that is passed to createTopics(topics) would be:

Single Item in Topics Array

 "submission": 
 "id": 52,
 "artistID": 111,
 "title": "Sego Sucks",
 "Artist": 
 "name": "Sego"
 
 ,
 "users": [
 
 "id": 7,
 "userUID": "ZvOBNBqxbgRYoibSYEwkL9YKtWG2"
 
 ]
 

My question is, when I run the forEach loop, I have an observable in findUserDevices that is iterated over several times really quickly, will my observable be "overwritten" by the next loop if it doesn't return a value before the next loop comes about? So far when I run this code, it executes as planned, but I am not sure if this is the best way to handle the observable as my data scales and there are more users per topic especially since pushToDevices() is an async function.

function createTopics(topics) 
 topics.forEach((topic: any) => 
 const message = 
 notification: 
 title: `New music from $topic.submission.Artist.name!`,
 body: `Listen to "$topic.submission.title" now`
 
 

 topic.users.forEach((user) => 
 findUserDevices(user.userUID, message);
 )
 )


function findUserDevices(uid: string, message) 
 collectionData(fb.firestore().collection('devices').where('userId', '==', uid)).subscribe((devices: any) => 
 var userDeviceTokens: string[] = devices.map((device: any) => device.token);
 if (userDeviceTokens.length != 0) 
 message['tokens'] = userDeviceTokens;
 pushToDevices(message);
 
 )


async function pushToDevices(message) 
 await admin.messaging().sendMulticast(message).then((response) => 
 console.log('done!')
 )

Thanks for any insight!

javascript typescript rxjs

share|improve this question

asked Mar 25 at 17:56

Jordan LewallenJordan Lewallen

54244 silver badges1212 bronze badges

 "submission": 
 "id": 52,
 "artistID": 111,
 "title": "Sego Sucks",
 "Artist": 
 "name": "Sego"
 
 ,
 "users": [
 
 "id": 7,
 "userUID": "ZvOBNBqxbgRYoibSYEwkL9YKtWG2"
 
 ]
 

function createTopics(topics) 
 topics.forEach((topic: any) => 
 const message = 
 notification: 
 title: `New music from $topic.submission.Artist.name!`,
 body: `Listen to "$topic.submission.title" now`
 
 

 topic.users.forEach((user) => 
 findUserDevices(user.userUID, message);
 )
 )


function findUserDevices(uid: string, message) 
 collectionData(fb.firestore().collection('devices').where('userId', '==', uid)).subscribe((devices: any) => 
 var userDeviceTokens: string[] = devices.map((device: any) => device.token);
 if (userDeviceTokens.length != 0) 
 message['tokens'] = userDeviceTokens;
 pushToDevices(message);
 
 )


async function pushToDevices(message) 
 await admin.messaging().sendMulticast(message).then((response) => 
 console.log('done!')
 )

share|improve this question

asked Mar 25 at 17:56

Jordan LewallenJordan Lewallen

54244 silver badges1212 bronze badges

share|improve this question

asked Mar 25 at 17:56

Jordan LewallenJordan Lewallen

54244 silver badges1212 bronze badges

asked Mar 25 at 17:56

Jordan LewallenJordan Lewallen

54244 silver badges1212 bronze badges

asked Mar 25 at 17:56

Jordan LewallenJordan Lewallen

54244 silver badges1212 bronze badges