JSFiddle - React, Tailwind, and code Playground

HTML

<span id="discount" data-discount='0.00'>0.00</span>
<span id='increment'>.10</span>
<a href="#" id="btn">Add!</a>

JavaScript

$(function() {
 $('a#btn').click(function() { 
 var discount = 0.0;
 var increment = 0.1;
 var newDiscountVal = (discount + increment).toFixed(2);
 $("span#discount").text(newDiscountVal);
 $("#discount").data("discount", newDiscountVal);
    });

});