rxjs

问题 I have a BehaviorSubject which emits JavaScript objects periodically. I want to construct another observable which will emit both previous and current values of the underlying observable in order to compare two objects and determine the delta. The pairwise() or bufferCount(2, 1) operators are looking like a good fit, but they start emitting only after buffer is filled, but I require this observable to start emitting from the first event of the underlying observable. subject

问题 I have a BehaviorSubject which emits JavaScript objects periodically. I want to construct another observable which will emit both previous and current values of the underlying observable in order to compare two objects and determine the delta. The pairwise() or bufferCount(2, 1) operators are looking like a good fit, but they start emitting only after buffer is filled, but I require this observable to start emitting from the first event of the underlying observable. subject

问题 The title says it all really. How can I get the current value from an Observable without subscribing to it? I just want the current value one time and not new values as they are coming in... 回答1: You need to use BehaviorSubject, BehaviorSubject is similar to ReplaySubject except it only remembers the last publication. BehaviorSubject also requires you to provide it a default value of T. This means that all subscribers will receive a value immediately (unless it is already completed). It will

问题 Note this is simplified question of Angular template binding with Observable async pipe issue template: <div>{{foo()$ | async}}</div> source code: import { Component } from "@angular/core"; import { BehaviorSubject, of, Observable } from "rxjs"; import { tap, delay, map, switchMap, concatMap } from "rxjs/operators"; @Component({ selector: "my-app", templateUrl: "./app.component.html", styleUrls: ["./app.component.css"] }) export class AppComponent { private index = 0; foo$(): Observable<any>

问题 I have a child component with a timer, every 2 second I send api call to the server. I need to do this call as long as the user is on the page even if he/she going to a wedding and leave the page (the parent compoent window) open. Here is some code from my component: this.myTimer = Observable.timer(1, 2000); this.myTimer .mergeMapTo(this.myService.doSomeWork(this.myId)) .subscribe((data) => { this.myData = data; }, (errRes)=>{ console.log(errRes); }); And here is the destroy method:

问题 I am learning angular and i got confuse in these observable, observer and subscribe thing. So please explain. 回答1: Here is a simple visual to see the difference: As seen above ... an Observable is a stream of events or data. They are often returned from Angular methods, such as the http.get and the myinputBox.valueChanges . Subscribing "kicks off" the observable stream. Without a subscribe (or an async pipe) the stream won't start emitting values. It's similar to subscribing to a newspaper or

问题 I am learning angular and i got confuse in these observable, observer and subscribe thing. So please explain. 回答1: Here is a simple visual to see the difference: As seen above ... an Observable is a stream of events or data. They are often returned from Angular methods, such as the http.get and the myinputBox.valueChanges . Subscribing "kicks off" the observable stream. Without a subscribe (or an async pipe) the stream won't start emitting values. It's similar to subscribing to a newspaper or

问题 I have a event emitter that I want to emit an object to a parent component however the event emitter is not emitting in the subscriber function Code categories = []; @Output() filteredCategory = new EventEmitter<any>(); @Output() maxiumPriceEmitter = new EventEmitter<any>(); categorySub: Subscription; formatLabel(value: number) { return 'R' + value; } constructor(private shopService: ShopService) {} ngOnInit() { this.initCategories(); this.filterCategories(); this.updateCategories(); }

问题 I have a event emitter that I want to emit an object to a parent component however the event emitter is not emitting in the subscriber function Code categories = []; @Output() filteredCategory = new EventEmitter<any>(); @Output() maxiumPriceEmitter = new EventEmitter<any>(); categorySub: Subscription; formatLabel(value: number) { return 'R' + value; } constructor(private shopService: ShopService) {} ngOnInit() { this.initCategories(); this.filterCategories(); this.updateCategories(); }

问题 I have a problem which is relevant to rxJS and bulk HTTP requests from the huge collection (1M+ docs) I have the following code, with quite simple logic. I push all the docs from the collection to allplayers array and making bulk 20 HTTP requests to API at once (guess you understand why it's limited) So, the code works fine, but I guess it's time to refactor it from this: const cursor = players_db.find(query).lean().cursor(); cursor.on('data', function(player) { allPlayers.push(player); });