jquery-watch.js

(function($) {

    $.fn.watch = function(callback, once) {   

        var options = {
            childList: true, 
            subtree: true
        };

        var _callOnNode = function() {
            callback.call(this);
        };

        var _mutationHandler = function(mutations, observer) {

            $.each(mutations, function() {

                $.each(this.removedNodes, _callOnNode);
                $.each(this.addedNodes, _callOnNode);
            });

            if (once) {
                observer.disconnect();
            }
        };

        $(this).each(function() {
            var observer = new MutationObserver(_mutationHandler);

            observer.observe(this, options);
        });

        return this;
    };
})(window.jQuery);

jQuery watch

Watch an element for descendants to be be added or removed. Takes an event handler as argument where this refers to the element being added or removed, and optionally a boolean which can be set to true if changes should be observed only once (i.e. the handler will get disconnected after the first observed change).

Sample usage

$('body').watch(function() {
    $(this).addClass('dynamic-content');
}).append('<div/>');