JSFiddle - React, Tailwind, and code Playground

JavaScript

window.onload = function () {alert(1)};

window.onload = (function (oldOnLoad) {
    return function () {
        if (oldOnLoad) {
            oldOnLoad();
        }
        alert(2);
    }
})(window.onload);

window.onload = (function (oldOnLoad) {
    return function () {
        if (oldOnLoad) {
            oldOnLoad();
        }
        alert(3);
    }
})(window.onload);