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angulartypescriptobservable
Adrien Brunelat
Adrien Brunelat

Reputation: 4642

How can I create an observable with a delay

Question

For testing purposes, I'm creating Observable objects that replace the observable that would be returned by an actual http call with Http.

My observable is created with the following code:

fakeObservable = Observable.create(obs => {
  obs.next([1, 2, 3]);
  obs.complete();
});

The thing is, this observable emits immediatly. Is there a way to add a custom delay to its emission?

Track

I tried this:

fakeObservable = Observable.create(obs => {
  setTimeout(() => {
    obs.next([1, 2, 3]);
    obs.complete();
  }, 100);
});

But it doesn't seem to work.

Upvotes: 149

Views: 219274

Answers (6)

Jayampathy Wijesena
Jayampathy Wijesena

Reputation: 1740

You can use asyncScheduler, it schedules tasks asynchronously, by putting them on the JavaScript event loop queue. It is best used to delay tasks in time or to schedule tasks repeating in intervals.

Link to the documentation

Upvotes: 0

Adrian Ber
Adrian Ber

Reputation: 21360

In RxJS 5+ you can do it like this 

import { Observable } from "rxjs/Observable";
import { of } from "rxjs/observable/of";
import { delay } from "rxjs/operators";

fakeObservable = of('dummy').pipe(delay(5000));

In RxJS 6+

import { of } from "rxjs";
import { delay } from "rxjs/operators";

fakeObservable = of('dummy').pipe(delay(5000));

If you want to delay each emitted value try

from([1, 2, 3]).pipe(concatMap(item => of(item).pipe(delay(1000))));

Upvotes: 173

MikeOne
MikeOne

Reputation: 4912

Using the following imports:

import {Observable} from 'rxjs/Observable';
import 'rxjs/add/observable/of';
import 'rxjs/add/operator/delay';

Try this:

let fakeResponse = [1,2,3];
let delayedObservable = Observable.of(fakeResponse).delay(5000);
delayedObservable.subscribe(data => console.log(data));

UPDATE: RXJS 6

The above solution doesn't really work anymore in newer versions of RXJS (and of angular for example).

So the scenario is that I have an array of items to check with an API with. The API only accepts a single item, and I do not want to kill the API by sending all requests at once. So I need a timed release of items on the Observable stream with a small delay in between.

Use the following imports:

import { from, of } from 'rxjs';
import { delay } from 'rxjs/internal/operators';
import { concatMap } from 'rxjs/internal/operators';

Then use the following code:

const myArray = [1,2,3,4];

from(myArray).pipe(
        concatMap( item => of(item).pipe ( delay( 1000 ) ))
    ).subscribe ( timedItem => {
        console.log(timedItem)
    });

It basically creates a new 'delayed' Observable for every item in your array. There are probably many other ways of doing it, but this worked fine for me, and complies with the 'new' RXJS format.

Upvotes: 209

Pellet
Pellet

Reputation: 2437

What you want is a timer:

// RxJS v6+
import { timer } from 'rxjs';

//emit [1, 2, 3] after 1 second.
const source = timer(1000).map(([1, 2, 3]);
//output: [1, 2, 3]
const subscribe = source.subscribe(val => console.log(val));

Upvotes: 19

Narendra Kumar Achari
Narendra Kumar Achari

Reputation: 5

import * as Rx from 'rxjs/Rx';

We should add the above import to make the blow code to work

Let obs = Rx.Observable
    .interval(1000).take(3);

obs.subscribe(value => console.log('Subscriber: ' + value));

Upvotes: -2

microchip78
microchip78

Reputation: 2060

It's little late to answer ... but just in case may be someone return to this question looking for an answer

'delay' is property(function) of an Observable

fakeObservable = Observable.create(obs => {
  obs.next([1, 2, 3]);
  obs.complete();
}).delay(3000);

This worked for me ...

Upvotes: 8

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