比如，停止事件冒泡IE用 cancelBubble ，标准浏览器则用 stopPropagation 。
获取事件源对象，IE用 srcElement ，标准浏览器则用 target 诸如此类。
jQuery 对原生事件对象的修复和包装主要使用 jQuery.Event 类和 jQuery.event.fix 方法。
复制代码 代码如下:
jQuery.Event = function( src ) {
// Allow instantiation without the 'new' keyword
if ( !this.preventDefault ) {
return new jQuery.Event( src );
}
// Event object
if ( src && src.type ) {
this.originalEvent = src;
this.type = src.type;
// Events bubbling up the document may have been marked as prevented
// by a handler lower down the tree; reflect the correct value.
this.isDefaultPrevented = (src.defaultPrevented || src.returnValue === false ||
src.getPreventDefault && src.getPreventDefault()) ? returnTrue : returnFalse;
// Event type
} else {
this.type = src;
}
// timeStamp is buggy for some events on Firefox(#3843)
// So we won't rely on the native value
this.timeStamp = jQuery.now();
// Mark it as fixed
this[ jQuery.expando ] = true;
};
function returnFalse() {
return false;
}
function returnTrue() {
return true;
}
// jQuery.Event is based on DOM3 Events as specified by the ECMAScript Language Binding
//
jQuery.Event.prototype = {
preventDefault: function() {
this.isDefaultPrevented = returnTrue;
var e = this.originalEvent;
if ( !e ) {
return;
}
// if preventDefault exists run it on the original event
if ( e.preventDefault ) {
e.preventDefault();
// otherwise set the returnValue property of the original event to false (IE)
} else {
e.returnValue = false;
}
},
stopPropagation: function() {
this.isPropagationStopped = returnTrue;
var e = this.originalEvent;
if ( !e ) {
return;
}
// if stopPropagation exists run it on the original event
if ( e.stopPropagation ) {
e.stopPropagation();
}
// otherwise set the cancelBubble property of the original event to true (IE)
e.cancelBubble = true;
},
stopImmediatePropagation: function() {
this.isImmediatePropagationStopped = returnTrue;
this.stopPropagation();
},
isDefaultPrevented: returnFalse,
isPropagationStopped: returnFalse,
isImmediatePropagationStopped: returnFalse
};
jQuery.Event 类主要做了以下工作
1，扩充了 originalEvent 属性，该属性暂存了原生事件对象。
2，修复了 ，该属性IE6/7/8不支持，其它支持的各个浏览器中返回值也不同。
3，阻止DOM元素默认行为统一采用 preventDefault
4，停止事件冒泡统一采用 stopPropagation
5，实现或扩充了 DOM3事件 的几个方法：stopImmediatePropagation、isDefaultPrevented、isPropagationStopped、isImmediatePropagationStopped
此外，jQuery.Event的 写类方式 也较独特。它 使用隐藏的new创建对象 。
jQuery.event.fix方法 如下
复制代码 代码如下:
fix: function( event ) {
if ( event[ jQuery.expando ] ) {
return event;
}
// store a copy of the original event object
// and "clone" to set read-only properties
var originalEvent = event;
event = jQuery.Event( originalEvent );
for ( var i = this.props.length, prop; i; ) {
prop = this.props[ --i ];
event[ prop ] = originalEvent[ prop ];
}
// Fix target property, if necessary
if ( !event.target ) {
// Fixes #1925 where srcElement might not be defined either
event.target = event.srcElement || document;
}
// check if target is a textnode (safari)
if ( event.target.nodeType === 3 ) {
event.target = event.target.parentNode;
}
// Add relatedTarget, if necessary
if ( !event.relatedTarget && event.fromElement ) {
event.relatedTarget = event.fromElement === event.target ? event.toElement : event.fromElement;
}
// Calculate pageX/Y if missing and clientX/Y available
if ( event.pageX == null && event.clientX != null ) {
var doc = document.documentElement,
body = document.body;
event.pageX = event.clientX + (doc && doc.scrollLeft || body && body.scrollLeft || 0) - (doc && doc.clientLeft || body && body.clientLeft || 0);
event.pageY = event.clientY + (doc && doc.scrollTop || body && body.scrollTop || 0) - (doc && doc.clientTop || body && body.clientTop || 0);
}
// Add which for key events
if ( event.which == null && (event.charCode != null || event.keyCode != null) ) {
event.which = event.charCode != null ? event.charCode : event.keyCode;
}
// Add metaKey to non-Mac browsers (use ctrl for PC's and Meta for Macs)
if ( !event.metaKey && event.ctrlKey ) {
event.metaKey = event.ctrlKey;
}
// Add which for click: 1 === left; 2 === middle; 3 === right
// Note: button is not normalized, so don't use it
if ( !event.which && event.button !== undefined ) {
event.which = (event.button & 1 ? 1 : ( event.button & 2 ? 3 : ( event.button & 4 ? 2 : 0 ) ));
}
return event;
},
它主要做了以下工作
1，event = jQuery.Event( originalEvent ); 该句创建了一个jQuery.Event类的实例对象，该对象修复及扩充上面刚刚提到了。
2， 一个循环将原生事件对象的所有属性拷贝给 1 中的event对象。
复制代码 代码如下: