JSFiddle - React, Tailwind, and code Playground

HTML

<input id="amount" name="amount" type="text" value="0" />
<input id="discount" name="discount" type="text" value="0" />
<input id="result" name="discount" type="text" value="0" />

JavaScript

$('input').focus(function () {
    $("#result").val(parseInt($("#amount").val(), 10) - parseInt($("#discount").val(), 10));
});