Jquery增加鼠标中间功能mousewheel的实例代码

代码如下:
(function ($) {
    var types = ['DOMMouseScroll', 'mousewheel'];
    $.event.special.mousewheel = {
        setup: function () {
            if (this.addEventListener) {
                for (var i = types.length; i;) {
                    this.addEventListener(types[--i], handler, false);
                }
            } else {
                this.onmousewheel = handler;
            }
        },
        teardown: function () {
            if (this.removeEventListener) {
                for (var i = types.length; i;) {
                    this.removeEventListener(types[--i], handler, false);
                }
            } else {
                this.onmousewheel = null;
            }
        }
    };
    $.fn.extend({
        mousewheel: function (fn) {
            return fn ? this.bind("mousewheel", fn) : this.trigger("mousewheel");
        },
        unmousewheel: function (fn) {
            return this.unbind("mousewheel", fn);
        }
    });

    function handler(event) {
        var orgEvent = event || window.event, args = [].slice.call(arguments, 1), delta = 0, returnValue = true, deltaX = 0, deltaY = 0;
        event = $.event.fix(orgEvent);
        event.type = "mousewheel";
        // Old school scrollwheel delta
        if (event.originalEvent.wheelDelta) { delta = event.originalEvent.wheelDelta / 120; }