Extend Typeahead (Twitter Bootstrap) with an onshow function. When initializing Typeahead, allows for defining onshow: function() {}.

gistfile1.js

(function($) {
	if($.fn.typeahead != 'undefined') {
		var _show = $.fn.typeahead.Constructor.prototype.show;

		$.fn.typeahead.Constructor.prototype.show = function() {
			if(typeof this.options.onshow == 'function') {
				this.options.onshow();
			}

			// Call parent
			_show.apply(this, []);
		};
	}
}(window.jQuery));