滚轮事件是一个非常有用的事件，在翻页或放大时，通常都用到它。但它在各浏览器中实现兼容是相对比较困难的，号称最标准的FF，用了一个私有实现DOMMouseScroll，而使用mousewheel的其他浏览器或多或少有点bug。我们先看各浏览器对它的支持程度吧。
| IE | firefox | safari | chrome | opera | |
|---|---|---|---|---|---|
| window对象 | false | true | true | true | true |
| 文档对象 | true | true | true | true | true |
| 元素节点 | true | true | true | true | true |
接着我们看一下，如何在火狐中实现滚轮事件的事件分派：
window.addEventListener("DOMMouseScroll",function(event){
alert(event.type)
alert(event.clientY)
},false);
var event = document.createEvent("MouseEvent");
//为了证明分派成功，特意将其clientY设为90
event.initMouseEvent("DOMMouseScroll",true, null, window,0,0,0,0,90,false,false,false,false,0,null);
window.dispatchEvent(event)
我们可以看到虽然其他标准浏览器也支持这个名为DOMMouseScroll的事件发派，但当我们手动滚动鼠标滑轮时，也只有FF有反应，弹出两个alert。对于其他标准浏览器，我们改用mousewheel试试。
window.addEventListener("mousewheel",function(event){
alert(event.type)
alert(event.clientX)
},false);
var event = document.createEvent("MouseEvent");
//为了证明分派成功，特意将其clientX设为120
event.initMouseEvent("mousewheel",true, null, window,0,0,0,120,0,false,false,false,false,0,null);
window.dispatchEvent(event)
这个在FF的以外的标准浏览器见效，FF只能实现事件分派，不能实现手动触发。可以说，如果非原浏览器原生支持的事件类型，addEventListener是一概不理会的。
对于IE就简单得多了，它没有初始化事件的步骤，你也无法设置其属性，因为那是只读的，但可以设置自定义属性。
window.onload = function(){
document.attachEvent("onmousewheel",function(){
var e = window.event;
alert(e)
alert(e.type)
alert(e.aa)
});
var event = document.createEventObject();
event.aa = "司徒正美"
document.fireEvent("onmousewheel",event)
}
说完事件分派，就到事件绑定部分。虽然现在只有FF在用DOMMouseScroll，但考虑到未来FF改用的mousewheel的可能，我们还是写个程序来检测其需要的事件类型吧。最后我们还要在回调函数中修正其滚动属性：
- IE6-11,chrome的属性名为wheelDelta，ff那边为detail，现在统一为delta。
- IE6-11等往上滚一圈为120，往下滚一圈为-120。ff那边往上滚一圈为-3，往下滚一圈为3，但opera9x系列却实现错误，与IE滚动方向一致，不过10后又修复。
- safari早期版本，wheelDelta会出现浮点数的情况，我们需要自行取整。
function addEvent(el, type, callback, useCapture ){
if(el.dispatchEvent){//w3c方式优先
el.addEventListener( type, callback, !!useCapture );
}else {
el.attachEvent( "on"+type, callback );
}
return callback;//返回callback方便卸载时用
}
var wheel = function(obj,callback){
var wheelType = "mousewheel"
try{
document.createEvent("MouseScrollEvents")
wheelType = "DOMMouseScroll"
}catch(e){}
addEvent(obj, wheelType,function(event){
if ("wheelDelta" in event){//统一为±120，其中正数表示为向上滚动，负数表示向下滚动
var delta = event.wheelDelta
//opera 9x系列的滚动方向与IE保持一致，10后修正
if( window.opera && opera.version() < 10 )
delta = -delta;
//由于事件对象的原有属性是只读，我们只能通过添加一个私有属性delta来解决兼容问题
event.delta = Math.round(delta) /120; //修正safari的浮点 bug
}else if( "detail" in event ){
event.wheelDelta = -event.detail * 40//为FF添加更大众化的wheelDelta
event.delta = event.wheelDelta /120 //添加私有的delta
}
callback.call(obj,event);//修正IE的this指向
});
}
用法：
wheel(document,function(e){
alert(e.delta)
});
| Event property | Applies to event: | Up 1 click | Up 2 clicks | Down 1 click | Down 2 clicks |
| e.wheelDelta Supported in Non FF browsers |
onmousewheel and in non FF
browsers |
120 | 240 | -120 | -240 |
| e.detail Supported in FF and Opera |
DOMMouseScroll and in FF
(as of FF3.x) |
-1 | -2 | 1 | 2 |
在FF官网还给出一个兼容方案：
// creates a global "addwheelListener" method
// example: addWheelListener( elem, function( e ) { console.log( e.deltaY ); e.preventDefault(); } );
(function(window,document) {
var prefix = "", _addEventListener, onwheel, support;
// detect event model
if ( window.addEventListener ) {
_addEventListener = "addEventListener";
} else {
_addEventListener = "attachEvent";
prefix = "on";
}
// detect available wheel event
if ( document.onmousewheel !== undefined ) {
// Webkit and IE support at least "mousewheel"
support = "mousewheel"
}
try {
// Modern browsers support "wheel"
WheelEvent("wheel");
support = "wheel";
} catch (e) {}
if ( !support ) {
// let's assume that remaining browsers are older Firefox
support = "DOMMouseScroll";
}
window.addWheelListener = function( elem, callback, useCapture ) {
_addWheelListener( elem, support, callback, useCapture );
// handle MozMousePixelScroll in older Firefox
if( support == "DOMMouseScroll" ) {
_addWheelListener( elem, "MozMousePixelScroll", callback, useCapture );
}
};
function _addWheelListener( elem, eventName, callback, useCapture ) {
elem[ _addEventListener ]( prefix + eventName, support == "wheel" ? callback : function( originalEvent ) {
!originalEvent && ( originalEvent = window.event );
// create a normalized event object
var event = {
// keep a ref to the original event object
originalEvent: originalEvent,
target: originalEvent.target || originalEvent.srcElement,
type: "wheel",
deltaMode: originalEvent.type == "MozMousePixelScroll" ? 0 : 1,
deltaX: 0,
delatZ: 0,
preventDefault: function() {
originalEvent.preventDefault ?
originalEvent.preventDefault() :
originalEvent.returnValue = false;
}
};
// calculate deltaY (and deltaX) according to the event
if ( support == "mousewheel" ) {
event.deltaY = - 1/40 * originalEvent.wheelDelta;
// Webkit also support wheelDeltaX
originalEvent.wheelDeltaX && ( event.deltaX = - 1/40 * originalEvent.wheelDeltaX );
} else {
event.deltaY = originalEvent.detail;
}
// it's time to fire the callback
return callback( event );
}, useCapture || false );
}
})(window,document);
| firefox | chrome | IE11 | safari5.1.7 | |
| wheel |
deltaX 0
deltaY 3(向下)
deltaZ 0
|
deltaX: -0
deltaY: 100
deltaZ: 0
detail: 0
wheelDelta: -120
wheelDeltaX: 0
wheelDeltaY: -120
|
deltaX: 0
deltaY: 52.5
deltaZ: 0
detail: 0
|
|
| mousewheel |
type竟然是wheel
deltaX: -0
deltaY: 100
deltaZ: 0
detail: 0
wheelDelta: -120
wheelDeltaX: 0
wheelDeltaY: -120
|
wheelDelta:-120 |
wheelDelta: -120
wheelDeltaX: 0
wheelDeltaY: -120
|
|
| DOMMouseScroll | detail:3(向下) |