typescript - RxJS delay at least X milliseconds -

i'm trying implement following behavior in rxjs:

1. fire event
2. call http api
3. when api returns, either:
   1. wait until @ least x milliseconds have passed since firing event
   2. return if x milliseconds have passed since firing event

this useful ux, because if call takes 1ms, i'd show loading icon @ least 100ms.

i haven't found way implement either delay, throttle, debounce or variations.

this.eventthatfires     .switchmap(data => {         let starttime = date.now();         return this.callhttpservice(data)             .delay(new date(starttime + 1000));     }) 

i assumed worked, using absolute date seems time difference current time, , not schedule delay absolute time.

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edit:

it seems there's no built-in operator works describe. created because i'll using lot throughout application:

import { observable } "rxjs/observable";  function delayatleast<t>(this: observable<t>, delay: number): observable<t> {     return observable.combinelatest(         observable.timer(delay),         this)     .map(([_, i]) => i); }  observable.prototype.delayatleast = delayatleast;  declare module "rxjs/observable" {     interface observable<t> {         delayatleast: typeof delayatleast;     } } 

effectively delay date same delay number, difference delay duration computed difference of specified date , current time.

you can use delaywhen operator compute delay when value emitted:

this.eventthatfires     .switchmap(data => {         let starttime = date.now();         return this.callhttpservice(data)             .delaywhen(() => rx.observable.timer(500 + starttime - date.now()))     })