Behavior Subject unsubscribe refactor

Question

This can't be the only way to unsub Behavior Subjects :

  maxSub;
  fromSub;
  toSub;
  pageNumberSub;
  originalMaxSub;
  selectionSub;
  selectionOfInterestSub;

  constructor(private store: StoreService) {}

  ngAfterContentChecked(){
    this.maxSub = this.store.max$.subscribe((max) => {
      if(max !== null && max !== undefined){
        this.max = max;
        this.maxPages = Math.floor(this.max / Variables.to);
        this.pages = Array.from(Array(this.maxPages), (x, i) => i + 1);
      }
    }, (error) => console.log(error), () => {});

    this.fromSub = this.store.from$.subscribe((from) => {
      if(from !== null && from !== undefined) {this.from = from; this.split = this.to - (this.from - 1)}
    }, (error) => console.log(error), () => {});

    this.toSub = this.store.to$.subscribe((to) => {
      if(to !== null && to !== undefined) {this.to = to; this.split = this.to - (this.from - 1)}
    }, (error) => console.log(error), () => {});

    this.pageNumberSub = this.store.pageNumber$.subscribe((pageNumber) => {
      if(pageNumber !== null && pageNumber !== undefined) {this.page = pageNumber;}
    }, (error) => console.log(error), () => {});

    this.originalMaxSub = this.store.originalMax$.subscribe((originalMax) => {
      if(originalMax !== null && originalMax !== undefined) {this.originalMax = originalMax;}
    }, (error) => console.log(error), () => {});

    this.selectionSub = this.store.selection$.subscribe((selection) => {
      if(selection !== null && selection !== undefined) this.selectedAmount = selection.length;
    }, (error) => console.log(error), () => {});

    this.selectionOfInterestSub = this.store.selectionOfInterest$.subscribe((selectionOfInterest) => {
      if(selectionOfInterest !== null && selectionOfInterest !== undefined) this.selectionOfInterest = selectionOfInterest;
    }, (error) => console.log(error), () => {});
  }

  ngOnDestroy(){
    this.maxSub.unsubscribe();
    this.fromSub.unsubscribe();
    this.toSub.unsubscribe();
    this.pageNumberSub.unsubscribe();
    this.originalMaxSub.unsubscribe();
    this.selectionSub.unsubscribe();
    this.selectionOfInterestSub.unsubscribe();
  }

in regular old Observables you can just :

alive = true;

constructor(private store: StoreService) {}

  ngAfterContentChecked(){
     this.store.thing.subscribe().takeWhile(this.alive)...
  }

  ngOnDestroy(){
    this.alive = false;
  }

which is much simpler.

Isn't there a way to do the same with Behavior Subjects?

Another thing : am I missing a fundamental property of Behavior Subjects that they only subscribe once within an class no matter how many times the subscribe is called and that's why there's no such thing as takeWhile() on Behavior Subjects?

Answer 1

1 - Actually what you call it a simpler way does not unsubscribe at all it just stop reading what comes from the observable. So either use unsubscribe or complete.

2 - Since you are unsubscribing at the same time and you clearluy don't use the Subject for anything else, then it's fine to use the same Subject variable for all your subs and then you can unsubscribe with oneline of code and you don't need to initialize all these Subject instances.