js鼠标滑轮滚动事件绑定（兼容主流浏览器）

/** Event handler for mouse wheel event.
                 *鼠标滚动事件
                 */
                var wheel = function(event) {
                        var delta = 0;
                        if (!event) /* For IE. */
                                event = window.event;
                        if (event.wheelDelta) { /* IE/Opera. */
                                delta = event.wheelDelta / 120;
                        } else if (event.detail) {
                                /** Mozilla case. */
                                /** In Mozilla, sign of delta is different than in IE.
                                 * Also, delta is multiple of 3.
                                 */
                                delta = -event.detail / 3;
                        }
                        /** If delta is nonzero, handle it.
                         * Basically, delta is now positive if wheel was scrolled up,
                         * and negative, if wheel was scrolled down.
                         */
                        if (delta)
                                handle(delta);
                        /** Prevent default actions caused by mouse wheel.
                         * That might be ugly, but we handle scrolls somehow
                         * anyway, so don't bother here..
                         */
                        if (event.preventDefault)
                                event.preventDefault();
                        event.returnValue = false;
                }

                /** Initialization code. 
                 * If you use your own event management code, change it as required.
                 */
                if (window.addEventListener) {
                        /** DOMMouseScroll is for mozilla. */
                        window.addEventListener('DOMMouseScroll', wheel, false);
                }
                /** IE/Opera. */
                window.onmousewheel = document.onmousewheel = wheel;

                /** This is high-level function.
                 * It must react to delta being more/less than zero.
                 */
                var handle = function(delta) {
                        var random_num = Math.floor((Math.random() * 100) + 50);
                        if (delta < 0) {
                                // alert("鼠标滑轮向下滚动：" + delta + "次！"); // 1
                                $("btn_next_pic").onclick(random_num);
                                return;
                        } else {
                                // alert("鼠标滑轮向上滚动：" + delta + "次！"); // -1
                                $("btn_last_pic").onclick(random_num);
                                return;
                        }
                }