Custom RXJS Operator : delayFirstEmmisionBy
Oct 14, 2020 11:22 · 33 words · 1 minute read
I ran accross an use case when first emmision needed to be delayed by X seconds and therefore had to resort to making my own custom operator.
Take first emmision and then resubscribe
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| import { MonoTypeOperatorFunction, Observable, Observer, Operator, TeardownLogic } from 'rxjs'; | |
| import { delay, take, switchMapTo } from 'rxjs/operators'; | |
| // defining operator as class must implement call method | |
| class DelayFirstEmmisionOperator<T> implements Operator<T, T> { | |
| constructor(private delayInMs:number) { } | |
| call(observer: Observer<T>, source: Observable<T>): TeardownLogic { | |
| return source.pipe( | |
| delay(this.delayInMs), | |
| take(1), | |
| // complete and then resubscribe to intial observable | |
| switchMapTo(source) | |
| ).subscribe(observer); | |
| } | |
| } | |
| /** Delay first emmision by passed amount of milliseconds and then continue */ | |
| export function delayFirstEmmisionBy<T>(delayInMs: number = 1000): MonoTypeOperatorFunction<T> { | |
| return source => source.lift(new DelayFirstEmmisionOperator(delayInMs)); | |
| } |