Return an empty Observable

Question

The function more   is supposed to return an Observable from a get request  export class Collection       public more       Observable lt Response gt    gt           if  this hasMore                return this fetch                    else              return empty observable                     private fetch       Observable lt Response gt    gt           return this http get  some-url   map             res    gt                  return res json                                    In this case I can only do a request if hasMore   is true  else I get an error on subscribe   function subscribe is not defined  how can I return an empty observable   this collection more   subscribe      res    gt          console log res             err    gt          console log err            Update  In RXJS 6  import   EMPTY   from  rxjs   return EMPTY

User · Answer

Came here with a similar question  the above didn t work for me in   rxjs     6 0 0   in order to generate an observable that emits no data I needed to do   import  Observable empty  from  rxjs   class ActivatedRouteStub     params  Observable lt any gt    empty

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You can return Observable of empty variable   for example  Observable of          or Observable of          etc

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Yes  there is am Empty operator  Rx Observable empty      For typescript  you can use from   Rx Observable lt Response gt  from

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Or you can try ignoreElements   as well

User · Answer

In my case with Angular2 and rxjs  it worked with   import  EmptyObservable  from  rxjs observable EmptyObservable       return new EmptyObservable

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Try this  export class Collection  public more     Observable lt Response gt       if  this hasMore           return this fetch            else       return this returnEmpty                          public returnEmpty    any       let subscription   source subscribe        function  x           console log  Next   s   x              function  err           console log  Error   s   err              function             console log  Completed                      let source   Observable empty

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For typescript you can specify generic param of your empty observable like this    import  rxjs add observable empty    Observable empty lt Response gt

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RxJS 6  you can use also from function like below   return from lt string gt           after import   import  from  from  rxjs

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With the new syntax of RxJS 5 5   this becomes as the following     RxJS 6 import   EMPTY  empty  of   from  quot rxjs quot       rxjs 5 5    lt 6  import   empty   from  quot rxjs observable empty quot   import   of   from  quot rxjs observable of quot    empty       deprecated use EMPTY EMPTY  of       Just one thing to keep in mind  EMPTY completes the observable  so it won t trigger next in your stream  but only completes  So if you have  for instance  tap  they might not get trigger as you wish  see an example below   Whereas of     creates an Observable and emits next with a value of    and then it completes the Observable  E g   EMPTY pipe      tap      gt  console warn  quot i will not reach here  as i am complete quot      subscribe     of     pipe      tap      gt  console warn  quot i will reach here and complete quot      subscribe

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RxJS6  without compatibility package installed  There s now an EMPTY constant and an empty function    import   Observable  empty  of   from  rxjs      var delay   empty   pipe delay 1000           var delay2   EMPTY pipe delay 1000     Observable empty   doesn t exist anymore

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Several ways to create an Empty Observable    They just differ on how you are going to use it further  what events it will emit after  next  complete or do nothing  e g     Observable never   - emits no events and never ends  Observable empty   - emits only complete  Observable of     - emits both next and complete  Empty object literal passed as an example     Use it on your exact needs

[javascript] Return an empty Observable

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