Combine two subjects in RxJS

Issue

In RxJS, how can I achieve this: I have two subjects. I want an observables that combines them in this way: When both have emitted values, emit the latest of their values. Then, both need to emit at least once again, then emit their latest emitted values, etc.

Both subjects:

1 ---------- 2 ----- 3 -- 4 ---------------- 5 ------ 6 -----------------

------- a ------------------ b ------ c --------------------- d --------

Goal observable:

------- 1a ----------------- 2b ----- 3c ------------------- 4d -------

Solution

This can be done with the zip function:

import { zip } from 'rxjs'

zip(subject1$, subject2$)
  .subscribe(([val1, val2]) => {
    console.log(`${val1}${val2}`);
  });

The term "zip" comes from zippers. The analogy is that a zipper pairs up successive teeth from each side of the zipper, so too the zip function pairs up successive values from the observables.

https://rxjs.dev/api/index/function/zip

Answered By - Nicholas Tower