let ready = false;

$(function() {
	ready = true;
});

var r$ = function(callback) {
	if (ready) {
		callback();
	} else {
		$(function() {
			callback();
		});
	}
}

function observe(containerSelector, elementSelector, callback) {
	r$(() => {

		$(containerSelector + ' ' + elementSelector).each(function (_, e) {
			let me = $(e);
			callback(me);
		});

		var onMutationsObserved = function(mutations) {
    	    mutations.forEach(function(mutation) {
    	        if (mutation.addedNodes.length) {
    	            var elements = $(mutation.addedNodes).find(elementSelector);
    	            for (var i = 0, len = elements.length; i < len; i++) {
						let me = elements[i];
						me = $(me);
						callback(me);
    	            }
    	        }
    	    });
    	};

    	var target = $(containerSelector)[0];
    	var config = { childList: true, subtree: true };
    	var MutationObserver = window.MutationObserver;
    	var observer = new MutationObserver(onMutationsObserved);
    	observer.observe(target, config);
	});
}