scrolltop 事件

解决在鼠标滚动过程中不断执行事件，在滚动完成之后再触发事件，用scrollstop。

(function () {

    var special = jQuery.event.special,
        uid1 = 'D' + (+new Date()),
        uid2 = 'D' + (+new Date() + 1);

    special.scrollstart = {
        setup: function () {

            var timer,
                handler = function (evt) {

                    var _self = this,
                        _args = arguments;

                    if (timer) {
                        clearTimeout(timer);
                    } else {
                        evt.type = 'scrollstart';
                        jQuery.event.dispatch.apply(_self, _args);
                    }

                    timer = setTimeout(function () {
                        timer = null;
                    }, special.scrollstop.latency);

                };

            jQuery(this).bind('scroll', handler).data(uid1, handler);

        },
        teardown: function () {
            jQuery(this).unbind('scroll', jQuery(this).data(uid1));
        }
    };

    special.scrollstop = {
        latency: 300,
        setup: function () {

            var timer,
                    handler = function (evt) {

                        var _self = this,
                        _args = arguments;

                        if (timer) {
                            clearTimeout(timer);
                        }

                        timer = setTimeout(function () {

                            timer = null;
                            evt.type = 'scrollstop';
                            jQuery.event.dispatch.apply(_self, _args);

                        }, special.scrollstop.latency);

                    };

            jQuery(this).bind('scroll', handler).data(uid2, handler);

        },
        teardown: function () {
            jQuery(this).unbind('scroll', jQuery(this).data(uid2));
        }
    };

})();