JSFiddle - React, Tailwind, and code Playground

HTML

<input id="input" type="number" value="0" />
<button id="plus" type="button">+</button>
<button id="minus" type="button">-</button>

JavaScript

function modify(direction) {
    var modifier = direction * 0.10;
    var next = Number($('#input').val()) + modifier;
    $('#input').val(next);
}

$('#plus').on('click', function () {
    modify(1);
});

$('#minus').on('click', function () {
    modify(-1);
});