为什么删除 BehaviourSubject 会导致我的服务延迟 3-4 秒？

Question

I had earlier created a BehaviourSubject and on subscribing it I was making a service call. But, due to the nature of BehaviorSubject , there was an unnecessary on the initialisation of the BehaviouSubject . So, on further reading, I changed BehaviourSubjedct to ReplaySubject(1) .

Now, In the main @Injectable class where I have defined the services, there is another service which is independent, that gets delayed once I made the above changes. How do I determine the cause of the issue here?

component.ts

constructor(private _subjectService: SubjectService, private _s1: Service1){
    this._s1.Call1();
    this.testFunction();
}

testFunction(){
this._subjectService.GetData().subscribe(res => {
      if (res !== null) {
         this._s1.Call2();  
     }
   }
}   

SubjectService

  // filterSubject = new BehaviorSubject(<KendoRequestVM>{});
  // filterDataSubject = new BehaviorSubject(<KendoRequestVM>{});

   filterSubject = new ReplaySubject<KendoRequestVM>(1);
   filterDataSubject = new ReplaySubject<KendoRequestVM>(1);

Here, Call1() is getting called when I use BehaviouSubject instead of ReplaySubject .

Answer 1

A behavior subject will always return immediately (synchronously even). A replay subject will only return immediately / synchronously if it has a value. It's impossible to tell with just the code you've shared because you haven't shared the part that is populating the subjects (eg calling next ) but that seems like the most likely explanation.