Angular RxJs When should I unsubscribe from Subscription

Question

When should I store the Subscription instances and invoke unsubscribe   during the NgOnDestroy life cycle and when can I simply ignore them  Saving all subscriptions introduces a lot of mess into component code  HTTP Client Guide ignore subscriptions like this  getHeroes       this heroService getHeroes                      subscribe                       heroes   gt  this heroes   heroes                       error   gt   this errorMessage    lt any gt error      In the same time Route  amp  Navigation Guide says that   Eventually  we ll navigate somewhere else  The router will remove this component from the DOM and destroy it  We need to clean up after ourselves before that happens  Specifically  we must unsubscribe before Angular destroys the component  Failure to do so could create a memory leak  We unsubscribe from our Observable in the ngOnDestroy method   private sub  any   ngOnInit       this sub   this route params subscribe params   gt         let id    params  id           converts string  id  to a number      this service getHero id  then hero   gt  this hero   hero             ngOnDestroy       this sub unsubscribe

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Based on   Using Class inheritance to hook to Angular 2 component lifecycle  Another generic approach    x000D   x000D  export abstract class UnsubscribeOnDestroy implements OnDestroy   x000D    protected d   Subject lt any gt   x000D   x000D    constructor     x000D      this d    new Subject lt void gt     x000D   x000D      const f   this ngOnDestroy  x000D      this ngOnDestroy        gt    x000D        f    x000D        this d  next    x000D        this d  complete    x000D         x000D      x000D   x000D    public ngOnDestroy     x000D         no-op x000D      x000D   x000D    x000D   x000D   x000D    And use     x000D   x000D   Component   x000D      selector   my-comp   x000D      template     x000D     x000D  export class RsvpFormSaveComponent extends UnsubscribeOnDestroy implements OnInit   x000D   x000D      constructor     x000D          super    x000D        x000D   x000D      ngOnInit    void   x000D        Observable of  bla   x000D         takeUntil this d   x000D         subscribe val   gt  console log val    x000D        x000D    x000D   x000D   x000D

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You usually need to unsubscribe when the components get destroyed  but Angular is going to handle it more and more as we go  for example in new minor version of Angular4  they have this section for routing unsubscribe      Do you need to unsubscribe  As described in the   ActivatedRoute  the one-stop-shop for route information section of the   Routing  amp  Navigation page  the Router manages the observables it   provides and localizes the subscriptions  The subscriptions are   cleaned up when the component is destroyed  protecting against memory   leaks  so you don t need to unsubscribe from the route paramMap   Observable    Also the example below is a good example from Angular to create a component and destroy it after  look at how component implements OnDestroy  if you need onInit  you also can implements it in your component  like implements OnInit  OnDestroy  import   Component  Input  OnDestroy   from   angular core     import   MissionService   from    mission service   import   Subscription     from  rxjs Subscription     Component     selector   my-astronaut     template         lt p gt          astronaut     lt strong gt   mission   lt  strong gt         lt button          click   confirm             disabled    announced    confirmed  gt          Confirm        lt  button gt       lt  p gt          export class AstronautComponent implements OnDestroy      Input   astronaut  string    mission     lt no mission announced gt      confirmed   false    announced   false    subscription  Subscription     constructor private missionService  MissionService        this subscription   missionService missionAnnounced  subscribe        mission   gt            this mission   mission          this announced   true          this confirmed   false                 confirm         this confirmed   true      this missionService confirmMission this astronaut          ngOnDestroy            prevent memory leak when component destroyed     this subscription unsubscribe

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You don t need to have bunch of subscriptions and unsubscribe manually  Use Subject and takeUntil combo to handle subscriptions like a boss  import   Subject   from  quot rxjs quot  import   takeUntil   from  quot rxjs operators quot    Component     moduleId    moduleName    selector   quot my-view quot     templateUrl   quot    views view-route view html quot     export class ViewRouteComponent implements OnInit  OnDestroy     componentDestroyed   Subject lt boolean gt    new Subject      constructor private titleService  TitleService        ngOnInit         this titleService emitter1         pipe takeUntil this componentDestroyed           subscribe  data  any    gt           do something 1            this titleService emitter2         pipe takeUntil this componentDestroyed           subscribe  data  any    gt           do something 2                       this titleService emitterN         pipe takeUntil this componentDestroyed           subscribe  data  any    gt           do something N              ngOnDestroy         this componentDestroyed  next true      this componentDestroyed  complete           Alternative approach  which was proposed by  acumartini in comments  uses takeWhile instead of takeUntil  You may prefer it  but mind that this way your Observable execution will not be cancelled on ngDestroy of your component  e g  when you make time consuming calculations or wait for data from server   Method  which is based on takeUntil  doesn t have this drawback and leads to immediate cancellation of request  Thanks to  AlexChe for detailed explanation in comments  So here is the code   Component     moduleId    moduleName    selector   quot my-view quot     templateUrl   quot    views view-route view html quot     export class ViewRouteComponent implements OnInit  OnDestroy     alive  boolean   true    constructor private titleService  TitleService        ngOnInit         this titleService emitter1         pipe takeWhile      gt  this alive          subscribe  data  any    gt           do something 1            this titleService emitter2         pipe takeWhile      gt  this alive          subscribe  data  any    gt           do something 2                        this titleService emitterN         pipe takeWhile      gt  this alive          subscribe  data  any    gt           do something N              ngOnDestroy         this alive   false

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--- Edit 4 - Additional Resources  2018 09 01   In a recent episode of Adventures in Angular Ben Lesh and Ward Bell discuss the issues around how when to unsubscribe in a component  The discussion starts at about 1 05 30   Ward mentions right now there s an awful takeUntil dance that takes a lot of machinery and Shai Reznik mentions Angular handles some of the subscriptions like http and routing   In response Ben mentions that there are discussions right now to allow Observables to hook into the Angular component lifecycle events and Ward suggests an Observable of lifecycle events that a component could subscribe to as a way of knowing when to complete Observables maintained as component internal state   That said  we mostly need solutions now so here are some other resources    A recommendation for the takeUntil   pattern from RxJs core team member Nicholas Jamieson and a tslint rule to help enforce it  https   ncjamieson com avoiding-takeuntil-leaks  Lightweight npm package that exposes an Observable operator that takes a component instance  this  as a parameter and automatically unsubscribes during ngOnDestroy  https   github com NetanelBasal ngx-take-until-destroy  Another variation of the above with slightly better ergonomics if you are not doing AOT builds  but we should all be doing AOT now   https   github com smnbbrv ngx-rx-collector Custom directive  ngSubscribe that works like async pipe but creates an embedded view in your template so you can refer to the  unwrapped  value throughout your template  https   netbasal com diy-subscription-handling-directive-in-angular-c8f6e762697f   I mention in a comment to Nicholas  blog that over-use of takeUntil   could be a sign that your component is trying to do too much and that separating your existing components into Feature and Presentational components should be considered  You can then   async the Observable from the Feature component into an Input of the Presentational component  which means no subscriptions are necessary anywhere  Read more about this approach here  --- Edit 3 - The  Official  Solution  2017 04 09   I spoke with Ward Bell about this question at NGConf  I even showed him this answer which he said was correct  but he told me the docs team for Angular had a solution to this question that is unpublished  though they are working on getting it approved   He also told me I could update my SO answer with the forthcoming official recommendation   The solution we should all use going forward is to add a private ngUnsubscribe   new Subject    field to all components that have  subscribe   calls to Observables within their class code   We then call this ngUnsubscribe next    this ngUnsubscribe complete    in our ngOnDestroy   methods   The secret sauce  as noted already by  metamaker  is to call takeUntil this ngUnsubscribe  before each of our  subscribe   calls which will guarantee all subscriptions will be cleaned up when the component is destroyed   Example   import   Component  OnDestroy  OnInit   from   angular core      RxJs 6 x  import paths import   filter  startWith  takeUntil   from  rxjs operators   import   Subject   from  rxjs   import   BookService   from     books service     Component       selector   app-books       templateUrl     books component html     export class BooksComponent implements OnDestroy  OnInit       private ngUnsubscribe   new Subject         constructor private booksService  BookService           ngOnInit             this booksService getBooks                pipe                 startWith                     filter books   gt  books length  gt  0                  takeUntil this ngUnsubscribe                             subscribe books   gt  console log books             this booksService getArchivedBooks                pipe takeUntil this ngUnsubscribe                subscribe archivedBooks   gt  console log archivedBooks               ngOnDestroy             this ngUnsubscribe next            this ngUnsubscribe complete              Note  It s important to add the takeUntil operator as the last one to prevent leaks with intermediate observables in the operator chain   --- Edit 2  2016 12 28   Source 5  The Angular tutorial  the Routing chapter now states the following   The Router manages the observables it provides and localizes the subscriptions  The subscriptions are cleaned up when the component is destroyed  protecting against memory leaks  so we don t need to unsubscribe from the route params Observable   - Mark Rajcok  Here s a discussion on the Github issues for the Angular docs regarding Router Observables where Ward Bell mentions that clarification for all of this is in the works   --- Edit 1  Source 4  In this video from NgEurope Rob Wormald also says you do not need to unsubscribe from Router Observables  He also mentions the http service and ActivatedRoute params in this video from November 2016   --- Original Answer  TLDR   For this question there are  2  kinds of Observables - finite value and infinite value   http Observables produce finite  1  values and something like a DOM event listener Observables produce infinite values   If you manually call subscribe  not using async pipe   then unsubscribe from infinite Observables   Don t worry about finite ones  RxJs will take care of them   Source 1  I tracked down an answer from Rob Wormald in Angular s Gitter here   He states  i reorganized for clarity and emphasis is mine      if its a single-value-sequence  like an http request    the manual cleanup is unnecessary  assuming you subscribe in the controller manually       i should say  if its a sequence that completes   of which single value sequences  a la http  are one       if its an infinite sequence  you should unsubscribe which the async pipe does for you   Also he mentions in this youtube video on Observables that they clean up after themselves    in the context of Observables that complete  like Promises  which always complete because they are always producing 1 value and ending - we never worried about unsubscribing from Promises to make sure they clean up xhr event listeners  right     Source 2  Also in the Rangle guide to Angular 2 it reads     In most cases we will not need to explicitly call the unsubscribe method unless we want to cancel early or our Observable has a longer lifespan than our subscription  The default behavior of Observable operators is to dispose of the subscription as soon as  complete   or  error   messages are published  Keep in mind that RxJS was designed to be used in a  fire and forget  fashion most of the time    When does the phrase our Observable has a longer lifespan than our subscription apply   It applies when a subscription is created inside a component which is destroyed before  or not  long  before  the Observable completes   I read this as meaning if we subscribe to an http request or an observable that emits 10 values and our component is destroyed before that http request returns or the 10 values have been emitted  we are still ok   When the request does return or the 10th value is finally emitted the Observable will complete and all resources will be cleaned up   Source 3  If we look at this example from the same Rangle guide we can see that the Subscription to route params does require an unsubscribe   because we don t know when those params will stop changing  emitting new values    The component could be destroyed by navigating away in which case the route params will likely still be changing  they could technically change until the app ends  and the resources allocated in subscription would still be allocated because there hasn t been a completion

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The Subscription class has an interesting feature      Represents a disposable resource  such as the execution of an Observable  A Subscription has one important method  unsubscribe  that takes no argument and just disposes the resource held by the subscription    Additionally  subscriptions may be grouped together through the add   method  which will attach a child Subscription to the current Subscription  When a Subscription is unsubscribed  all its children  and its grandchildren  will be unsubscribed as well    You can create an aggregate Subscription object that groups all your subscriptions  You do this by creating an empty Subscription and adding subscriptions to it using its add   method  When your component is destroyed  you only need to unsubscribe the aggregate subscription    Component          export class SmartComponent implements OnInit  OnDestroy     private subscriptions   new Subscription       constructor private heroService  HeroService           ngOnInit         this subscriptions add this heroService getHeroes   subscribe heroes   gt  this heroes   heroes        this subscriptions add    another subscription          this subscriptions add    and another subscription          this subscriptions add    and so on             ngOnDestroy         this subscriptions unsubscribe

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Following the answer by  seangwright  I ve written an abstract class that handles  infinite  observables  subscriptions in components   import   OnDestroy   from   angular core   import   Subscription   from  rxjs Subscription   import   Subject   from  rxjs Subject   import   Observable   from  rxjs Observable   import   PartialObserver   from  rxjs Observer    export abstract class InfiniteSubscriberComponent implements OnDestroy     private onDestroySource  Subject lt any gt    new Subject       constructor         subscribe observable  Observable lt any gt    Subscription     subscribe      observable  Observable lt any gt       observer  PartialObserver lt any gt       Subscription     subscribe      observable  Observable lt any gt       next    value  any    gt  void      error    error  any    gt  void      complete        gt  void      Subscription     subscribe observable  Observable lt any gt      subscribeArgs   Subscription       return observable        takeUntil this onDestroySource         subscribe    subscribeArgs          ngOnDestroy         this onDestroySource next        this onDestroySource complete            To use it  just extend it in your angular component and call the subscribe   method as follows   this subscribe someObservable  data   gt  doSomething       It also accepts the error and complete callbacks as usual  an observer object  or not callbacks at all  Remember to call super ngOnDestroy   if you are also implementing that method in the child component   Find here an additional reference by Ben Lesh  RxJS  Don   t Unsubscribe

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The official Edit  3 answer  and variations  works well  but the thing that gets me is the  muddying  of the business logic around the observable subscription   Here s another approach using wrappers      Warining  experimental code   File subscribeAndGuard ts is used to create a new Observable extension to wrap  subscribe   and within it to wrap ngOnDestroy    Usage is the same as  subscribe    except for an additional first parameter referencing the component     import   Observable   from  rxjs Observable   import   Subscription   from  rxjs Subscription    const subscribeAndGuard   function component  fnData  fnError   null  fnComplete   null          Define the subscription   const sub  Subscription   this subscribe fnData  fnError  fnComplete         Wrap component s onDestroy   if   component ngOnDestroy        throw new Error  To use subscribeAndGuard  the component must implement ngOnDestroy          const saved OnDestroy   component ngOnDestroy    component ngOnDestroy        gt        console log  subscribeAndGuard onDestroy        sub unsubscribe           Note  need to put original back in place        otherwise  this  is undefined in component ngOnDestroy     component ngOnDestroy   saved OnDestroy      component ngOnDestroy             return sub         Create an Observable extension Observable prototype subscribeAndGuard   subscribeAndGuard      Ref  https   www typescriptlang org docs handbook declaration-merging html declare module  rxjs Observable      interface Observable lt T gt        subscribeAndGuard  typeof subscribeAndGuard          Here is a component with two subscriptions  one with the wrapper and one without  The only caveat is it must implement OnDestroy  with empty body if desired   otherwise Angular does not know to call the wrapped version   import   Component  OnInit  OnDestroy   from   angular core   import   Observable   from  rxjs Observable   import  rxjs Rx   import    subscribeAndGuard     Component     selector   app-subscribing     template    lt h3 gt Subscribing component is active lt  h3 gt       export class SubscribingComponent implements OnInit  OnDestroy      ngOnInit             This subscription will be terminated after onDestroy     Observable interval 1000         subscribeAndGuard this           data    gt    console log  Guarded    data               error    gt                  completed      gt                       This subscription will continue after onDestroy     Observable interval 1000         subscribe           data    gt    console log  Unguarded    data               error    gt                  completed      gt                      ngOnDestroy         console log  SubscribingComponent OnDestroy            A demo plunker is here  An additional note  Re Edit 3 - The  Official  Solution  this can be simplified by using takeWhile   instead of takeUntil   before subscriptions  and a simple boolean rather than another Observable in ngOnDestroy    Component        export class SubscribingComponent implements OnInit  OnDestroy      iAmAlive   true    ngOnInit          Observable interval 1000         takeWhile      gt    return this iAmAlive            subscribe  data    gt    console log data              ngOnDestroy         this iAmAlive   false

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I like the last two answers  but I experienced an issue if the the subclass referenced  this  in ngOnDestroy   I modified it to be this  and it looks like it resolved that issue     export abstract class BaseComponent implements OnDestroy       protected componentDestroyed   Subject lt boolean gt       constructor             this componentDestroyed    new Subject lt boolean gt             let f   this ngOnDestroy          this ngOnDestroy   function                     without this I was getting an error if the subclass had                this blah   in ngOnDestroy             f bind this                 this componentDestroyed  next true               this componentDestroyed  complete                             placeholder of ngOnDestroy  no need to do super   call of extended class      ngOnDestroy

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Since seangwright s solution  Edit 3  appears to be very useful  I also found it a pain to pack this feature into base component  and hint other project teammates to remember to call super   on ngOnDestroy to activate this feature   This answer provide a way to set free from super call  and make  componentDestroyed   a core of base component   class BaseClass       protected componentDestroyed   Subject lt void gt    new Subject lt void gt         constructor                  wrap the ngOnDestroy to be an Observable  and set free from calling super   on ngOnDestroy          let      this ngOnDestroy          this ngOnDestroy        gt                this componentDestroyed  next                this componentDestroyed  complete                                               placeholder of ngOnDestroy  no need to do super   call of extended class      ngOnDestroy          And then you can use this feature freely for example    Component       selector   my-thing       templateUrl     my-thing component html     export class MyThingComponent extends BaseClass implements OnInit  OnDestroy       constructor          private myThingService  MyThingService          super           ngOnInit             this myThingService getThings                takeUntil this componentDestroyed                subscribe things   gt  console log things                   optional  not a requirement to implement OnDestroy     ngOnDestroy             console log  everything works as intended with or without super call

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The SubSink package  an easy and consistent solution for unsubscribing  As nobody else has mentioned it  I want to recommend the Subsink package created by Ward Bell  https   github com wardbell subsink readme   I have been using it on a project were we are several developers all using it  It helps a lot to have a consistent way that works in every situation

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Another short addition to the above mentioned situations is    Always unsubscribe  when new values in the subscribed stream is no more required or don t matter  it will result in way less number of triggers and increase in performance in a few cases  Cases such as components where the subscribed data event no more exists or a new subscription to an all new stream is required  refresh  etc   is a good example for unsubscription

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--- Update Angular 9 and Rxjs 6 Solution   Using unsubscribe at ngDestroy lifecycle of Angular Component   class SampleComponent implements OnInit  OnDestroy     private subscriptions  Subscription    private sampleObservable   Observable lt any gt      constructor          ngOnInit        this subscriptions   this sampleObservable  subscribe                ngOnDestroy         this subscriptions unsubscribe             Using takeUntil in Rxjs   class SampleComponent implements OnInit  OnDestroy     private unsubscribe   new Subject lt void gt     private sampleObservable   Observable lt any gt      constructor          ngOnInit        this subscriptions   this sampleObservable       pipe takeUntil this unsubscribe         subscribe                ngOnDestroy         this unsubscribe  next        this unsubscribe  complete             for some action that you call at ngOnInit that just happen only one time when component init    class SampleComponent implements OnInit      private sampleObservable   Observable lt any gt      constructor          ngOnInit        this subscriptions   this sampleObservable       pipe take 1        subscribe                 We also have async pipe  But  this one use on the template  not in Angular component

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A lot of great answers here    Let me add another alternative  import   interval      from  quot rxjs quot   import   takeUntil     from  quot rxjs operators quot   import   Component     from  quot  angular core quot   import   Destroyable   from  quot  bespunky angular-zen core quot     Component       selector   app-no-leak-demo       template    Destroyable component rendered  Unload me and watch me cleanup        export class NoLeakComponent extends Destroyable       constructor                 super             this subscribeToInterval               private subscribeToInterval    void               const value      interval 1000           const observer                 next      value   gt  console log   Destroyable    value                 complete          gt  console log   Observable completed                                Comment one and uncomment the other to see the difference                          Subscribe using the inherited subscribe method          this subscribe value  observer                   or pipe-in the inherited destroyed subject           value pipe takeUntil this destroyed   subscribe observer            Live Example What s happening here The component service extends Destroyable  which comes from a library called  bespunky angular-zen   The class can now simply use this subscribe   or takeUntil this destroyed  without any additional boilerplate code   To install the library use   gt  npm install  bespunky angular-zen

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In my case I am using a variation of the solution proposed by  seanwright  https   github com NetanelBasal ngx-take-until-destroy It s a file used in the ngx-rocket   starter-kit project  You can access it here until-destroyed ts The component would look like so        RxJS operator that unsubscribe from observables on destory     Code forked from https   github com NetanelBasal ngx-take-until-destroy       IMPORTANT  Add the  untilDestroyed  operator as the last one to    prevent leaks with intermediate observables in the    operator chain         param instance The parent Angular component or object instance      param destroyMethodName The method to hook on  default   ngOnDestroy        import   untilDestroyed   from        core until-destroyed     Component     selector   app-example     templateUrl     example component html     export class ExampleComponent implements OnInit  OnDestroy      ngOnInit         interval 1000           pipe untilDestroyed this            subscribe val   gt  console log val                           This method must be present  even if empty    ngOnDestroy            To protect you  an error will be thrown if it doesn t exist

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in SPA application at ngOnDestroy function  angular lifeCycle  For each subscribe you need to unsubscribe it  advantage    to prevent the state from becoming too heavy   for example  in component1    import  UserService  from    user service    private user    name   test   id  1   constructor public userService  UserService        this userService onUserChange next this user       in service   import  BehaviorSubject  from  rxjs BehaviorSubject    public onUserChange  BehaviorSubject lt any gt    new BehaviorSubject        in component2   import  Subscription  from  rxjs Subscription   import  UserService  from    user service    private onUserChange  Subscription   constructor public userService  UserService        this onUserChange   this userService onUserChange subscribe user   gt            console log user              public ngOnDestroy    void          note  Here you have to be sure to unsubscribe to the subscribe item      this onUserChange unsubscribe

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I tried seangwright s solution  Edit 3   That is not working for Observable that created by timer or interval   However  i got it working by using another approach   import   Component  OnDestroy  OnInit   from   angular core   import  rxjs add operator takeUntil   import   Subject   from  rxjs Subject   import   Subscription   from  rxjs Subscription   import  rxjs Rx    import   MyThingService   from     my-thing service     Component      selector   my-thing      templateUrl     my-thing component html     export class MyThingComponent implements OnDestroy  OnInit      private subscriptions  Array lt Subscription gt           constructor       private myThingService  MyThingService              ngOnInit         const newSubs   this myThingService getThings            subscribe things   gt  console log things        this subscriptions push newSubs          ngOnDestroy         for  const subs of this subscriptions          subs unsubscribe

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In case unsubscribe is needed the following operator for observable pipe method can be used  import   Observable  Subject   from  rxjs   import   takeUntil   from  rxjs operators   import   OnDestroy   from   angular core    export const takeUntilDestroyed    componentInstance  OnDestroy    gt   lt T gt  observable  Observable lt T gt     gt      const subjectPropertyName      takeUntilDestroySubject       const originalOnDestroy   componentInstance ngOnDestroy    const componentSubject   componentInstance subjectPropertyName  as Subject lt any gt     new Subject       componentInstance ngOnDestroy       args    gt        originalOnDestroy apply componentInstance  args       componentSubject next true       componentSubject complete            return observable pipe takeUntil lt T gt  componentSubject         it can be used like this   import   Component  OnDestroy  OnInit   from   angular core   import   Observable   from  rxjs     Component   template    lt div gt  lt  div gt      export class SomeComponent implements OnInit  OnDestroy      ngOnInit    void       const observable   Observable create observer   gt          observer next  Hello                 observable        pipe takeUntilDestroyed this          subscribe val   gt  console log val           ngOnDestroy    void           The operator wraps ngOnDestroy method of component   Important  the operator should be the last one in observable pipe

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Some of the best practices regarding observables unsubscriptions inside Angular components   A quote from Routing  amp  Navigation     When subscribing to an observable in a component  you almost always arrange to unsubscribe when the component is destroyed       There are a few exceptional observables where this is not necessary  The ActivatedRoute observables are among the exceptions       The ActivatedRoute and its observables are insulated from the Router itself  The Router destroys a routed component when it is no longer needed and the injected ActivatedRoute dies with it       Feel free to unsubscribe anyway  It is harmless and never a bad practice    And in responding to the following links     1  Should I unsubscribe from Angular 2 Http Observables   2  Is it necessary to unsubscribe from observables created by Http methods   3  RxJS  Don   t Unsubscribe  4  The easiest way to unsubscribe from Observables in Angular  5  Documentation for RxJS Unsubscribing  6  Unsubscribing in a service is kind of pointless since there is no chance of memory leaks  7  Do we need to unsubscribe from observable that completes errors-out   8  A comment about the http observable   I collected some of the best practices regarding observables unsubscriptions inside Angular components to share with you    http observable unsubscription is conditional and we should consider the effects of the  subscribe callback  being run after the component is destroyed on a case by case basis  We know that angular unsubscribes and cleans the http observable itself  1    2   While this is true from the perspective of resources it only tells half the story  Let s say we re talking about directly calling http from within a component  and the http response took longer than needed so the user closed the component  The subscribe   handler will still be called even if the component is closed and destroyed  This can have unwanted side effects and in the worse scenarios leave the application state broken  It can also cause exceptions if the code in the callback tries to call something that has just been disposed of  However at the same time occasionally they are desired  Like  let s say you re creating an email client and you trigger a sound when the email is done sending - well you d still want that to occur even if the component is closed  8   No need to unsubscribe from observables that complete or error  However  there is no harm in doing so 7   Use AsyncPipe as much as possible because it automatically unsubscribes from the observable on component destruction  Unsubscribe from the ActivatedRoute observables like route params if they are subscribed inside a nested  Added inside tpl with the component selector  or dynamic component as they may be subscribed many times as long as the parent host component exists  No need to unsubscribe from them in other scenarios as mentioned in the quote above from Routing  amp  Navigation docs  Unsubscribe from global observables shared between components that are exposed through an Angular service for example as they may be subscribed multiple times as long as the component is initialized  No need to unsubscribe from internal observables of an application scoped service since this service never get s destroyed  unless your entire application get s destroyed  there is no real reason to unsubscribe from it and there is no chance of memory leaks   6   Note  Regarding scoped services  i e component providers  they are destroyed when the component is destroyed  In this case  if we subscribe to any observable inside this provider  we should consider unsubscribing from it using the OnDestroy lifecycle hook which will be called when the service is destroyed  according to the docs  Use an abstract technique to avoid any code mess that may be resulted from unsubscriptions  You can manage your subscriptions with takeUntil  3  or you can use this npm package mentioned at  4  The easiest way to unsubscribe from Observables in Angular  Always unsubscribe from FormGroup observables like form valueChanges and form statusChanges Always unsubscribe from observables of Renderer2 service like renderer2 listen Unsubscribe from every observable else as a memory-leak guard step until Angular Docs explicitly tells us which observables are unnecessary to be unsubscribed  Check issue   5  Documentation for RxJS Unsubscribing  Open    Bonus  Always use the Angular ways to bind events like HostListener as angular cares well about removing the event listeners if needed and prevents any potential memory leak due to event bindings    A nice final tip  If you don t know if an observable is being automatically unsubscribed completed or not  add a complete callback to subscribe      and check if it gets called when the component is destroyed

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It depends  If by calling someObservable subscribe    you start holding up some resource that must be manually freed-up when the lifecycle of your component is over  then you should call theSubscription unsubscribe   to prevent memory leak   Let s take a closer look at your examples   getHero   returns the result of http get    If you look into the angular 2 source code  http get   creates two event listeners    xhr addEventListener  load   onLoad    xhr addEventListener  error   onError     and by calling unsubscribe    you can cancel the request as well as the listeners    xhr removeEventListener  load   onLoad    xhr removeEventListener  error   onError    xhr abort      Note that  xhr is platform specific but I think it s safe to assume that it is an XMLHttpRequest   in your case   Normally  this is enough evidence to warrant a manual unsubscribe   call  But according this WHATWG spec  the XMLHttpRequest   is subject to garbage collection once it is  done   even if there are event listeners attached to it  So I guess that s why angular 2 official guide omits unsubscribe   and lets GC clean up the listeners   As for your second example  it depends on the implementation of params  As of today  the angular official guide no longer shows unsubscribing from params  I looked into src again and found that params is a just a BehaviorSubject  Since no event listeners or timers were used  and no global variables were created  it should be safe to omit unsubscribe     The bottom line to your question is that always call unsubscribe   as a guard against memory leak  unless you are certain that the execution of the observable doesn t create global variables  add event listeners  set timers  or do anything else that results in memory leaks   When in doubt  look into the implementation of that observable  If the observable has written some clean up logic into its unsubscribe    which is usually the function that is returned by the constructor  then you have good reason to seriously consider calling unsubscribe

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A Subscription essentially just has an unsubscribe   function to release resources or cancel Observable executions  In Angular  we have to unsubscribe from the Observable when the component is being destroyed  Luckily  Angular has a ngOnDestroy hook that is called before a component is destroyed  this enables devs to provide the cleanup crew here to avoid hanging subscriptions  open portals  and what nots that may come in the future to bite us in the back  Component        export class AppComponent implements OnInit  OnDestroy       subscription  Subscription      ngOnInit              var observable   Rx Observable interval 1000           this subscription   observable subscribe x   gt  console log x              ngOnDestroy             this subscription unsubscribe            We added ngOnDestroy to our AppCompoennt and called unsubscribe method on the this subscription Observable If there are multiple subscriptions   Component        export class AppComponent implements OnInit  OnDestroy       subscription1   Subscription     subscription2   Subscription      ngOnInit              var observable1    Rx Observable interval 1000           var observable2    Rx Observable interval 400           this subscription1    observable subscribe x   gt  console log  quot From interval 1000 quot  x            this subscription2    observable subscribe x   gt  console log  quot From interval 400 quot  x              ngOnDestroy             this subscription1  unsubscribe           this subscription2  unsubscribe

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For handling subscription I use a  Unsubscriber  class    Here is the Unsubscriber Class   export class Unsubscriber implements OnDestroy     private subscriptions  Subscription            addSubscription subscription  Subscription   Subscription          if  Array isArray subscription           this subscriptions push    subscription         else         this subscriptions push subscription                unsubscribe         this subscriptions        filter subscription   gt  subscription         forEach subscription   gt            subscription unsubscribe                     ngOnDestroy         this unsubscribe            And You can use this class in any component   Service   Effect etc   Example    class SampleComponent extends Unsubscriber       constructor              super               this addSubscription subscription

User · Answer

For observables that complete directly after emitting the result like AsyncSubject or for example observables from http requests and such you don t need to unsubscribe  It doesn t hurt to to call unsubscribe   for those  but if the observable is closed the unsubscribe method will simply not do anything  if  this closed      return     When you have long-lived observables that emit several values over time  like for example a BehaviorSubject or a ReplaySubject  you need to unsubscribe to prevent memory leaks  You can easily create an observable that completes directly after emitting a result from such long lived observables using a pipe operator  In some answers here the take 1  pipe is mentioned  But I prefer the first   pipe  The difference to take 1  is that it will   deliver an EmptyError to the Observer s error callback if the Observable completes before any next notification was sent   Another advantage of the first pipe is that you can pass a predicate that will help you to return the first value that satisfies certain criteria  const predicate    result  any    gt          check value and return true if it is the result that satisfies your needs   return true    observable pipe first predicate   subscribe observer    First will complete directly after emitting the first value  or when passing a function argument the first value that satisfies your predicate  so there is no need to unsubscribe  Sometimes you are not sure about whether you have a long lived observable or not  I am not saying it is good practice but you could then always add the first pipe just to make sure you won t need to manually unsubscribe  Adding an additional first pipe on an observable that will emit only one value doesn t hurt  During development you can use the single pipe that will fail if source observable emits several events  This can help you to explore the type of observable and whether it is necessary to unsubscribe from it or not  observable pipe single    subscribe observer    The first and single seem very similar  both pipes can take an optional predicate but the differences are important and nicely summarized in this stackoverflow answer here   First Will emit as soon as first item appears  Will complete right after that  Single Will fail if source observable emits several events    Note I tried to be as accurate and complete as possible in my answer with references to the official documentation  but please comment if something important is missing

User · Answer

Angular 2 official documentation provides an explanation for when to unsubscribe and when it can be safely ignored  Have a look at this link  https   angular io docs ts latest cookbook component-communication html   bidirectional-service Look for the paragraph with the heading Parent and children communicate via a service and then the blue box   Notice that we capture the subscription and unsubscribe when the AstronautComponent is destroyed  This is a memory-leak guard step  There is no actual risk in this app because the lifetime of a AstronautComponent is the same as the lifetime of the app itself  That would not always be true in a more complex application  We do not add this guard to the MissionControlComponent because  as the parent  it controls the lifetime of the MissionService   I hope this helps you

User · Answer

You can use latest Subscription class to unsubscribe for the Observable with not so messy code   We can do this with normal variable but it will be override the last subscription on every new subscribe so avoid that  and this approach is very much useful when you are dealing with more number of Obseravables  and type of Obeservables like BehavoiurSubject and Subject  Subscription     Represents a disposable resource  such as the execution of an Observable  A Subscription has one important method  unsubscribe  that takes no argument and just disposes the resource held by the subscription    you can use this in two ways    you can directly push the subscription to Subscription Array   subscriptions Subscription           ngOnInit    void       this subscription push this dataService getMessageTracker   subscribe  param  any    gt                                    this subscription push this dataService getFileTracker   subscribe  param  any    gt                                ngOnDestroy           prevent memory leak when component destroyed     this subscriptions forEach s   gt  s unsubscribe          using add   of Subscription  subscriptions   new Subscription     this subscriptions add subscribeOne   this subscriptions add subscribeTwo    ngOnDestroy       this subscriptions unsubscribe         A Subscription can hold child subscriptions and safely unsubscribe them all  This method handles possible errors  e g  if any child subscriptions are null     Hope this helps

[angular] Angular/RxJs When should I unsubscribe from `Subscription`

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