How to simplify the condition for the paginator?

Question

JavaScript

https://repl.it/@fomenkogregory/Paginator-5#src/App.js

I created such a paginator, how to simplify the condition without changing the behavior? Help.

Answer 1

Let's put into separate variables the conditions that determine whether it is necessary to show groups of buttons that ...

// ...прилегают к первой кнопке
const showAfterFirst = currentPage < 5;

// ...прилегают к последней кнопке
const showBeforeLast = currentPage > totalPages - 4;

Accordingly, the conditions for displaying ellipsis after/before the first/last buttons will be the reverse values: !showAfterFirstand !showBeforeLast. And to display the central group of buttons, both base conditions must be false: !(showAfterFirst || showBeforeLast).
https://jsfiddle.net/0sjgrcxu/1/