Demo:  endWith

endWith adds the given set of values to the end of the incoming stream.

endWith(x,y,z);

//Add the given set of values to the end of the data stream
let input_1 = of(50, 60, 80, 90).pipe(endWith(10,20,30)) ;

//Let's add 1 sec delay after each item to remove the overlaps
let process = concatMap(v => of(v).pipe(delay(1000)));

let output = input_1.pipe(process).subscribe(v=>console.log(v))