JSFiddle - React, Tailwind, and code Playground

HTML

<form>
  
  <INPUT TYPE=TEXT NAME="input_A" SIZE=15>
  
 <INPUT TYPE=TEXT NAME="input_B" 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="1221" />
  </form>

JavaScript

function CalculateIMSUB(form) {
    var Atext = form.input_A.value;

    var Btext = form.input_B.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;
    
    form.input_A.value = form.input_A.value.replace(/\+/g, ",");
    form.input_B.value = form.input_B.value.replace(/\+/g, ",");


}

function calculateAll() {
    var forms = document.getElementsByTagName("form");
    for (var i = 0; i < forms.length; i++) {
        CalculateIMSUB(forms[i])
    }
}