JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text" value="0" class="test" /><br />
<br />
<a class="click">Click</a>

CSS

a.click {
    cursor:pointer;
    display:block;
    width:100px;
    height:20px;
    text-align:center;
    background:#d4d4d4;
    border:1px solid #000;
    font-family:Verdana, sans-serif;
}

a.click:hover {
    background:#333;
    color:#ffffff;
}

JavaScript

$('a.click').click(function(event) {
    event.preventDefault();
    
    var currentValue = parseInt($('input.test').val());
    var step         = 0.5;
    var newValue     = currentValue + step;
    
    $('input.test').val(newValue);
});