JSFiddle - React, Tailwind, and code Playground

JavaScript

function detected() {
    var container = document.body;
    if (document.createElement &&
    container && container.appendChild && container.removeChild) {
        var el = document.createElement("div");
        if (!el.getBoundingClientRect) {
            return null;
        }
        el.innerHTML = "x";
        el.style.cssText = "position:fixed;top:100px;";
        container.appendChild(el);
        var originalHeight = container.style.height, originalScrollTop = container.scrollTop;
        container.style.height = "3000px";
        container.scrollTop = 500;
        var elementTop = el.getBoundingClientRect().top;
        container.style.height = originalHeight;
        var isSupported = elementTop === 100;
        container.removeChild(el);
        container.scrollTop = originalScrollTop;
        return isSupported;
    }
    return null;
};
if (detected()) {
    alert ('non-mobile');
} else {
    alert ('mobile');
}