Toggle Darkmode w/ a body class

darkmode-toggle.html

<a href='#' data-darkmode-btn>Toggle Darkmode</a>
<script type="text/javascript">
/* eslint-disable */
var darkModeBtn = document.querySelector('a[data-darkmode-btn]');
var bodyEle = document.querySelector('body');
if (localStorage.getItem('darkmode') === 'yes') {
    bodyEle.classList.add("darkmode");
}

function darkmodetoggle(e) {
    e.preventDefault();
    var darkmode = localStorage.getItem('darkmode');
    if (darkmode === "yes") {
        bodyEle.classList.remove("darkmode");
        localStorage.setItem('darkmode', 'no');
    } else {
        bodyEle.classList.add("darkmode");
        localStorage.setItem('darkmode', 'yes');
    }
    return;
}

darkModeBtn.addEventListener('click', darkmodetoggle);
</script>