How do I properly cache requests with RXjs?

Question

JavaScript

The situation is this.
There is a text. Every text change and I send a request. In the answer, the text is divided into parts.
Then I send each part to the server again.
Example:
Request - Response
1234567 => [1], [2], [3,4], [5, 6, 7]
Request queue
[1] => [2] => [3,4] => [5 ,6,7]
Change the text
Request - Answer
12334567 => [1], [2], [3,3,4], [5, 6, 7]
Here I want to compare the previous answer with the new one, weed out what is already there, to send only
[3, 3, 4]
I decided to make it all a stream, and finally deal with RxJS.
Actually looking for RxJS way