JSFiddle - React, Tailwind, and code Playground

HTML

<form>
    <INPUT TYPE=TEXT NAME="first" SIZE=15>
    <INPUT TYPE=TEXT NAME="second" SIZE=10>
    <INPUT TYPE="button" VALUE="+" name="SubtractButton" onclick="CalculateIMSUB(this.form)">
    <INPUT TYPE=TEXT NAME="Answer" SIZE=12>
    <input type="hidden" name="val" value="" />
</form>

JavaScript

function CalculateIMSUB(form) {
    var Atext = form.first.value;
    var Btext = form.second.value;
    var val = form.val.value;
    var A = eval(Atext);
    var B = eval(Btext);
    if (isNaN(A)) A = 0;
    if (isNaN(B)) B = 0;
    var answer = A - B;
    form.Answer.value = answer;
}