JSFiddle - React, Tailwind, and code Playground

HTML

<form>
    <input type="text" placeholder="First Name" required id="fname" name="fname" />
    <input type="text" placeholder="Last Name" required id="lname" name="lname" />
    <input type="checkbox" placeholder="Maiden Name" id="maidenname" name="chkname" />
</form>

JavaScript

var checkbox = document.getElementById('maidenname');
checkbox.addEventListener('click', function () {
    if (document.getElementById('mn')) {
        document.getElementById('mn').remove();
    } else {
        var input = document.createElement("input");
        input.id = 'mn';
        input.type = 'text';
        input.placeholder = 'Maiden Name';
        document.body.appendChild(input);
    }
});