How to trigger an rxjs observable

Question

Using rxjs v6

So I have multiple variables that I want to track/observe, and when any of them change, trigger an Observable to call an API, which then updates something else based on those variables.

I thought I could maybe trigger an event on a div to force the observable to do something, but it's not returning results based on what I want

E.g.

var a, b, c, d // if any updates, should trigger div "update" event

let obs = fromEvent(this.$refs.updater, "update")
    .pipe(
        switchMap(i => {return this.callAnAPI()})
    )
obs.subscribe()

var update = new Event("update")
this.$refs.updater.dispatchEvent(update)

However, there is no subscribe method on the observable. I was trying to modify one of my other Observables (which works)

fromEvent(input, "keyup")
    .pipe(
        map(i => i.currentTarget.value),
        debounceTime(delay),
        distinctUntilChanged(),
        switchMap(value => 
        {
            this.page = 1
            if (ajax)
            {
                return ajax
            }   
            else
            {
                return this.axiosAjax({
                    path,
                    method,
                    data: {
                        ...data,
                        [term]: value
                    }
                })
            }    
        })
    )

is update a custom event listener? because there is no event listener called update as far as I know — Jacob Goh
@JacobGoh Yes, I'll update with how I implemented it. Just an extra note that the Observable is created, but I just can't subscribe like I expect — A. L
Can you elaborate what you mean by "there is no subscribe method on the observable" and how the two snippets you posted interact? — Yoshi

Yoshi Yoshi · Accepted Answer · 2018-06-29T11:06:32

Based on the title of your question, I'm speculating that your custom event is just a means to an end.

If so, I don't think it's actually necessary. If you want "outside" influence (or a trigger) over an observable, use a Subject.

For example:

const { fromEvent, merge, of, Subject } = rxjs;
const { switchMap, delay } = rxjs.operators;

// fake api
const fakeApi$ = of(Math.random()).pipe(
  delay(2000),
);

// store a reference to the subject
const triggerApi$ = new Subject();

// apply behavior
const api$ = triggerApi$.pipe(
  switchMap(
    () => {
      console.log('switching to api call');

      // delegate to api call
      return fakeApi$;
    }
  )
);

// activate (handle result)
api$.subscribe((result) => {
  console.log('api result', result);
});

// some outside triggers
const fooClicks$ = fromEvent(document.getElementById('foo'), 'click');
const barClicks$ = fromEvent(document.getElementById('bar'), 'click');
const bazChanges$ = fromEvent(document.getElementById('baz'), 'change');

// combined
const updates$ = merge(fooClicks$, barClicks$, bazChanges$);

// activate
updates$.subscribe(triggerApi$);

<script src="https://unpkg.com/[email protected]/bundles/rxjs.umd.min.js"></script>

<button id="foo">foo</button>
<button id="bar">bar</button>
<textarea id="baz"></textarea>

How to trigger an rxjs observable

1 Answers