JSFiddle - React, Tailwind, and code Playground

HTML

<h1><b><i>Duncan Online Donut's Service</i></b></h1>
        <form>
            Name : <input id="name" type="text" name="name"/><br><br>
            #no of cake donuts : <input id="cakedonut" type="text" name="cakedonut" onchange="subTotal()"/><br><br>
            #no of glazed donuts : <input id="glazedonut" type="text" name="glazedonut" onchange="subTotal("/><br><br>
            subTotal : <input id="subTotal" type="text" name="subTotal" /><br><br>
            tax : <input id="tax" type="text" name="tax" /><br><br>
            Total : <input id="total" type="text" name="total"/><br><br>
            <input type="submit"/><br><br>
        </form>

JavaScript

function subTotal(){
            alert("working");
            const TAXRATE = 0.095;
            const DONUTRATE = 0.5;
            var tax = 0;
            var subTotal = 0;
            var total = 0;
            var cakedonut = parseInt(document.getElementById("cakedonut").value);
            var glazedonut = parseInt(document.getElementById("glazedonut").value);

            if(isNaN(cakedonut))
                cakedonut = 0;
            if(isNaN(glazedonut))
                glazedounut = 0;

            subTotal = (cakedonut + glazedonut)* DONUTRATE ;
            tax = subTotal * TAXRATE ;
            total = subTotal + tax ;
            document.getElementById("subTotal").value = "$" + subTotal.toFixed(2);
            document.getElementById("tax").value = "$" + tax.toFixed(2);
            document.getElementById("total").value = "$" + total.toFixed(2);    
        }