Best way to import Observable from rxjs

Question

In my angular 2 app I have a service that uses the Observable class from the rxjs library   import   Observable   from  rxjs     At the moment I am just using Observable so that I can use the toPromise   function   I read in another StackOverflow question somewhere that importing in this way and also importing from rxjs Rx will import a whole lot of unnecessary stuff from the rxjs library that will increase the page load times and or the code base   My question is  what is the best way to import Observable so I can use the toPromise   function without having to import everything else

User · Answer

One thing I ve learnt the hard way is being consistent  Watch out for mixing    import   BehaviorSubject   from  rxjs     with   import   BehaviorSubject   from  rxjs BehaviorSubject     This will probably work just fine UNTIL you try to pass the object to another class  where you did it the other way  and then this can fail    myBehaviorSubject instanceof Observable    It fails because the prototype chain will be different and it will be false    I can t pretend to understand exactly what is happening but sometimes I run into this and need to change to the longer format

User · Answer

Rxjs v 6    It got simplified with newer version of rxjs     1  Operators  import  map  from  rxjs operators     2  Others  import  Observable of  from   from  rxjs     Instead of chaining we need to pipe   For example   Old syntax    source map   switchMap   subscribe     New Syntax    source pipe map    switchMap    subscribe     Note  Some operators have a name change due to name collisions with JavaScript reserved words  These include    do -  tap    catch -  catchError  switch -  switchAll  finally -  finalize    Rxjs v 5    I am writing this answer partly to help myself as I keep checking docs everytime I need to import an operator   Let me know if something can be done better way    1  import   Rx   from  rxjs Rx    This imports the entire library  Then you don t need to worry about loading each operator   But you need to append Rx  I hope tree-shaking will optimize and pick only needed funcionts  need to verify   As mentioned in comments   tree-shaking can not help  So this is not optimized way     public cache   new Rx BehaviorSubject          Or you can import individual operators     This will Optimize your app to use only those files     2  import             from  rxjs              This syntax usually used for main Object like Rx itself or Observable etc     Keywords which can be imported with this syntax    Observable  Observer  BehaviorSubject  Subject  ReplaySubject   3  import  rxjs add observable               Update for Angular 5  With Angular 5  which uses rxjs 5 5 2    import   empty   from  rxjs observable empty   import   concat  from  rxjs observable concat     These are usually accompanied with Observable directly  For example  Observable from   Observable of     Other such keywords which can be imported using this syntax    concat  defer  empty  forkJoin  from  fromPromise  if  interval  merge  of   range  throw  timer  using  zip   4  import  rxjs add operator              Update for Angular 5  With Angular 5  which uses rxjs 5 5 2    import   filter   from  rxjs operators filter   import   map   from  rxjs operators map     These usually come in the stream after the Observable is created  Like flatMap in this code snippet    Observable of  1 2 3 4              flatMap arr   gt  Observable from arr      Other such keywords using this syntax    audit  buffer  catch  combineAll  combineLatest  concat  count  debounce  delay   distinct  do  every  expand  filter  finally  find   first  groupBy  ignoreElements  isEmpty  last  let  map  max  merge  mergeMap  min  pluck   publish  race  reduce  repeat  scan  skip  startWith  switch  switchMap  take   takeUntil  throttle  timeout  toArray  toPromise  withLatestFrom  zip   FlatMap   flatMap is alias to mergeMap so we need to import mergeMap to use flatMap      Note for  add imports     We only need to import once in whole project  So its advised to do it at a single place  If they are included in multiple files  and one of them is deleted  the build will fail for wrong reasons

User · Answer

Update for RxJS 6  April 2018   It is now perfectly fine to import directly from rxjs   As can be seen in Angular 6    Importing from rxjs operators is also fine and it is actually no longer possible to import operators globally  one of major reasons for refactoring rxjs 6 and the new approach using pipe   Thanks to this treeshaking can now be used as well   Sample code from rxjs repo   import   Observable  Subject  ReplaySubject  from  of  range   from  rxjs   import   map  filter  switchMap   from  rxjs operators    range 1  200     pipe filter x   gt  x   2     1   map x   gt  x   x      subscribe x   gt  console log x      Backwards compatibility for rxjs  lt  6   rxjs team released a compatibility package on npm that is pretty much install  amp  play  With this all your rxjs 5 x code should run without any issues  This is especially useful now when most of the dependencies  i e  modules for Angular  are not yet updated

[angular] Best way to import Observable from rxjs

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