Chaining Observables in RxJS

Question

I m learning RxJS and Angular 2  Let s say I have a promise chain with multiple async function calls which depend on the previous one s result which looks like    var promiseChain   new Promise  resolve  reject    gt      setTimeout      gt        resolve 1        1000      then  result    gt      console log result      return new Promise  resolve  reject    gt        setTimeout      gt          resolve result   2          1000            then  result    gt      console log result      return new Promise  resolve  reject    gt          setTimeout      gt          resolve result   3              1000              promiseChain then  finalResult    gt      console log finalResult         My attempts at doing the same solely using RxJS without the use of promises produced the following   var observableChain   Observable create  observer    gt      setTimeout      gt        observer next 1       observer complete         1000      flatMap  result    gt      console log result      return Observable create  observer    gt        setTimeout      gt          observer next result   2         observer complete          1000            flatMap  result    gt      console log result      return Observable create  observer    gt        setTimeout      gt          observer next result   3         observer complete          1000              observableChain subscribe  finalResult    gt      console log finalResult         It yields the same output as the promise chain  My questions are   Am I doing this right  Are there any RxJS related improvements that I can make to the above code How do I get this observable chain to execute repeatedly  i e  Adding another subscription at the end just produces an additional 6 though I expect it to print 1  3 and 6   observableChain subscribe  finalResult         console log finalResult        observableChain subscribe  finalResult         console log finalResult        1 3 6 6

User · Accepted Answer

About promise composition vs  Rxjs  as this is a frequently asked question  you can refer to a number of previously asked questions on SO  among which     How to do the chain sequence in rxjs RxJS Promise Composition  passing data  RxJS sequence equvalent to promise then      Basically  flatMap is the equivalent of Promise then   For your second question  do you want to replay values already emitted  or do you want to process new values as they arrive  In the first case  check the publishReplay operator  In the second case  standard subscription is enough  However you might need to be aware of the cold  vs  hot dichotomy depending on your source  cf  Hot and Cold observables   are there   39 hot  39  and   39 cold  39  operators  for an illustrated explanation of the concept

[javascript] Chaining Observables in RxJS

Examples related to javascript

Examples related to promise

Examples related to reactive-programming

Examples related to rxjs

Examples related to rxjs5