The point of this operator is to stitch as many values together as possible. We may be dealing with continuous streams, but also with streams that have a limit to the number of values they emit. You use this operator in the following way:

// combination/zip.js

let stream$ = Rx.Observable.of(1, 2, 3, 4);
let secondStream$ = Rx.Observable.of(5, 6, 7, 8);
let thirdStream$ = Rx.Observable.of(9, 10); 

let zippedStream$ = Rx.Observable.zip(
  stream$,
  secondStream$,
  thirdStream$
)

// [1, 5, 9] [2, 6, 10]
zippedStream$.subscribe(data => console.log(data))

As we can see, here, we stitch values together vertically, and by the least common denominator, thirdStream$ is the shortest, calculating the number of emitted values. This means we will take values from left to right and zip them together. As thirdStream$ only has two values, we end up with only two emits.