JSFiddle - React, Tailwind, and code Playground

HTML

Начислить: <input class="maddings" />   <input type="button" id="btn" value="Add" /><br>
<br>
    Всего: <input id="mtotal" class="maddings" />

JavaScript

$("#btn").click(function() {
            var sum = 0;

            $("input[class *= 'maddings']").each(function () {
                
                sum += +$(this).val();
            });

            $("#mtotal").val(sum);
        });