attach.js

/**
 * Custom plugin to find if an object already has an event handler and also to attach
 * event handlers only if not already attached.
 */
(function ($) {

    /**
     * Attaches an event handler only if not already attached.
     * @param {any} type The event type, such as 'click' or 'keyup'.
     * @param {any} handler The function handler.
     */
    $.fn.attach = function (type, handler) {
        // Only attach if not already on element
        if (!$(this).isAttached(type, handler)) {
            $(this).on(type, handler);
        }
    };

    /**
     * Determines if a handler is attached for an event on an element.
     * @param {any} type The event type, such as 'click' or 'keyup'.
     * @param {any} handler The function handler.
     */
    $.fn.isAttached = function (type, handler) {

        var found = false;
        this.each(function () {
            var events = $._data($(this)[0], "events");
            for (var prop in events) {
                if (Object.prototype.hasOwnProperty.call(events, prop)) {
                    var event = events[prop][0];
                    if (event.type === type && typeof (handler) === "undefined") {
                        // The event type, such as 'keyup' is attached but we are not
                        // comparing the function. The event is attached.
                        found = true;
                    }

                    if (event.type === type && typeof (handler) !== "undefined") {

                        // Compare the function
                        var comparer = event.handler.toString().replace(/\s/g, "") === handler.toString().replace(/\s/g, "");

                        // We compare on function level as well
                        // and they are the same. The event is attached.
                        if (comparer) {
                            found = true;
                        }
                    }
                }
            }
        });

        // The event was not found
        return found;
    };

}(jQuery));