Observable emit only one value using Delay within ConcatMap

问题

Having the following code:

range(1, 30)
  .pipe(
    windowCount(10),
    concatMap(x => x.pipe(delay(5000))),
  )
  .subscribe(console.log);

For some reason only the first value is emitted (1..10), Could someone point out what's wrong with the above code? Thanks.

expected output: 1..10 (delay) 11..20 (delay) and so on....

回答1:

This is happening because windowCount will complete the previous inner "window" before creating a new one. You delay each "window" by 5s but when concatMap wants to subscribe to the next "window" it has completed already and will never ever emit anything.

Note, that windowCount will emit all windows asap regardless whether concatMap had even chance to subscribe to them.

回答2:

I ended up using bufferCount and expected output is achieved.

range(1, 30)
  .pipe(
    bufferCount(10),
    concatMap(x => x.pipe(delay(5000))),
  )
  .subscribe(console.log);

DEMO

来源：https://stackoverflow.com/questions/62813365/observable-emit-only-one-value-using-delay-within-concatmap