JSFiddle - React, Tailwind, and code Playground

HTML

<form id="panda" method="post">
    <input type="submit" value="The Panda says..."/>
</form>

JavaScript

// your function
var my_func = function(event) {
    alert("me and all my relatives are owned by China");
    event.preventDefault();
};

// your form
var form = document.getElementById("panda");

// attach event listener
form.addEventListener("submit", my_func, true);