JSFiddle - React, Tailwind, and code Playground

HTML

<title>DPS</title>
<body>
    <form id="value-input">
        <input type="text" name="damage" id="damage" placeholder="Damage">
        <input type="text" name="firerate" id="firerate" placeholder="Firerate">
        <input type="button" id="submit" value="Calculate">
        <input type="reset">
    </form>
    <script src="main.js"></script>
</body>

JavaScript

function calc() {
    var damage = document.getElementById('damage');
    var firerate = document.getElementById('firerate');
    alert(newFirerate * newDamage);
}

document.querySelector('submit').addEventListener('onClick', calc);