JSFiddle - React, Tailwind, and code Playground

HTML

<form onsubmit="return show_confirm();" action="javascript:alert($('form').serialize() + ' would be send now.');">
    <input type="text" name="test" value="test"><br>
    <input type="submit" value="Show a confirm box">
</form>

JavaScript

function show_confirm() {
    var r=confirm("Press a button!");
    if (r===true) {
        alert("You pressed OK!");
    } else {
        alert("You pressed Cancel!");
        return false;
    }
}