JSFiddle - React, Tailwind, and code Playground

JavaScript

window.__intervals = [];

function wheneverIsAvailable(obj, prop, func) {
    var id = (Math.random()+"").substring(2);
    var args = arguments;
    window.__intervals[id] = window.setInterval(function() {
        if(obj.hasOwnProperty(prop)) {
            window.clearInterval(window.__intervals[id]);
            func(Array.prototype.slice.call(args, 3));
            // Call function with additional parameters passed
            // after func (from index 3 and on)
        }
    }, 1000/ 50);
}

wheneverIsAvailable(window, 'test', function() {
    alert(arguments[0]);
}, 'Woot!');

window.setTimeout('window.test = 123', 1000);