JSFiddle - React, Tailwind, and code Playground

HTML

<a href="#" class="prev">Prev</a>  <a href="#" class="next">Next</a>

JavaScript

var total = 6;
var currentIndex = 3;
var num = 0;
function add(amount) {
   return num = (num + total - currentIndex + amount) % total + 1
    
}


$('a').click(function(e){
    var num = e.target.className == 'prev' ? -1 : 1;
    var result = add(num)+currentIndex;
    console.log(result);
});