Demo:  max

The max operator finds the maximum number out of all the input numbers from the source and emits it as the source completes.

max();

//Each input is delayed by 1 sec
let input = of(50,15,20,12,30,90,30,60)
        .pipe(concatMap(v => of(v).pipe(delay(1000))))

//Find the max of all the input
let process = max();

let output=input.pipe(process).subscribe(v=>console.log(v))