兼容各浏览器的鼠标滚动事件写法

wheelEvent = "onwheel" in document.createElement("div") ? "wheel" : // Modern browsers support "wheel"

            document.onmousewheel !== undefined ? "mousewheel" : // Webkit and IE support at least "mousewheel"
            
            "DOMMouseScroll" // let‘s assume that remaining browsers are older Firefox