javascript事件之：jQuery.event.add事件详解

　　我们已经了解过jQuery.event下的方法，回顾一下

jQuery.event = {
    global: {},
    add: function( elem, types, handler, data, selector ) {},
    remove: function( elem, types, handler, selector, mappedTypes ) {},
    trigger: function( event, data, elem, onlyHandlers ) {},
    dispatch: function( event ) {},
    handlers: function( event, handlers ) {},
    props: "altKey bubbles cancelable ctrlKey currentTarget eventPhase metaKey relatedTarget shiftKey target timeStamp view which".split(" "),
    fixHooks: {},
    keyHooks: {
        props: "char charCode key keyCode".split(" "),
        filter: function( event, original ) {}
    },
    mouseHooks: {
        props: "button buttons clientX clientY offsetX offsetY pageX pageY screenX screenY toElement".split(" "),
        filter: function( event, original ) {}
    },
    fix: function( event ) {},
    special: {
        load: {
            noBubble: true
        },
        focus: {
            // Fire native event if possible so blur/focus sequence is correct
            trigger: function() {},
            delegateType: "focusin"
        },
        blur: {
            trigger: function() {},
            delegateType: "focusout"
        },
        click: {
            trigger: function() {},
            _default: function( event ) {
                return jQuery.nodeName( event.target, "a" );
            }
        },
        beforeunload: {
            postDispatch: function( event ) {}
        }
    },
    simulate: function( type, elem, event, bubble ) {}
}

今天，我们先来了解jQuery.event.add方法

我们先来看源码

/*　　elem: 操作的元素　　types: 事件类型　　handle: 事件触发的方法　　data: 事件触发的方法需要的参数　　selector: 委托的元素　　　　调用： 比如我们在jquery.fn.on中的调用　　jQuery.fn.extend({　　　　on: function(){　　　　　　...　　　　　　jQuery.event.add( this, types, fn, data, selector );　　　　　　...　　　　}　　})*/add: function( elem, types, handler, data, selector ) {
    var handleObjIn, eventHandle, tmp,
        events, t, handleObj,
        special, handlers, type, namespaces, origType,　　　　　/*　　　　　获取绑定在elem上的data缓存　　　　　 */
        elemData = data_priv.get( elem );
　 　//不允许出现文本节或者注释节点。但允许出现空对象{}    if ( !elemData ) {
        return;
    }　　 //这里的handler允许是对象代替handler函数，这里的对象指的是下面的handlerObj。要我说这里有点累赘。干嘛要非得支持这种写法的多样性，增加阅读复杂度。　　if ( handler.handler ) {
        handleObjIn = handler;
        handler = handleObjIn.handler;
        selector = handleObjIn.selector;
    }　　//给handler添加一个guid属性，确保handler函数有唯一ID，之后的查找或者删除可以使用它
    if ( !handler.guid ) {
        handler.guid = jQuery.guid++;
    }

    // elemData如果没有events属性，给它加上。第一次才会用上
    if ( !(events = elemData.events) ) {
        events = elemData.events = {};
    }　　// elemData没有handle属性，给它加上    if ( !(eventHandle = elemData.handle) ) {
        eventHandle = elemData.handle = function( e ) {
            // Discard the second event of a jQuery.event.trigger() and
            // when an event is called after a page has unloaded
            return typeof jQuery !== core_strundefined && (!e || jQuery.event.triggered !== e.type) ?
                jQuery.event.dispatch.apply( eventHandle.elem, arguments ) :
                undefined;
        };
        // Add elem as a property of the handle fn to prevent a memory leak with IE non-native events
        eventHandle.elem = elem;
    }

    // 处理用空格分开的多事件操作
    types = ( types || "" ).match( core_rnotwhite ) || [""];
    t = types.length;
    while ( t-- ) {　　　　 //typenamespace = /^([^.]*)(?:\.(.+)|)$/;
        tmp = rtypenamespace.exec( types[t] ) || [];
        type = origType = tmp[1];
        namespaces = ( tmp[2] || "" ).split( "." ).sort();

        // There *must* be a type, no attaching namespace-only handlers
        if ( !type ) {
            continue;
        }

        // 得到特殊处理的事件类型
        special = jQuery.event.special[ type ] || {};

        // 如果selector有定义，type可能不一样
        type = ( selector ? special.delegateType : special.bindType ) || type;

        // 修正special
        special = jQuery.event.special[ type ] || {};

        // 得到handleObj
        handleObj = jQuery.extend({
            type: type,
            origType: origType,
            data: data,
            handler: handler,
            guid: handler.guid,
            selector: selector,
            needsContext: selector && jQuery.expr.match.needsContext.test( selector ),
            namespace: namespaces.join(".")
        }, handleObjIn );

        // 初始化elemData.events[type]
        if ( !(handlers = events[ type ]) ) {
            handlers = events[ type ] = [];
            handlers.delegateCount = 0;

            // 在没有special.setup或者special.setup返回false时候，对元素绑定事件
            if ( !special.setup || special.setup.call( elem, data, namespaces, eventHandle ) === false ) {
                if ( elem.addEventListener ) {
                    elem.addEventListener( type, eventHandle, false );
                }
            }
        }
　　　　//如果有special.add，执行special.add
        if ( special.add ) {
            special.add.call( elem, handleObj );
　　　　　　　//如果handleObj.handler.guid不存在，吧handler.grid赋值给handleObj.handler.guid
            if ( !handleObj.handler.guid ) {
                handleObj.handler.guid = handler.guid;
            }
        }

        // 把handleObj附加到events[type]数组。对于委托事件，delegateCount++并且添加到数组最前面。否则加到数组后面
        if ( selector ) {
            handlers.splice( handlers.delegateCount++, 0, handleObj );
        } else {
            handlers.push( handleObj );
        }

        // Keep track of which events have ever been used, for event optimization
        jQuery.event.global[ type ] = true;
    }

    // 让elem为空，避免ie内存泄露
    elem = null;
}

上面我们已经对jQuery.event.add的源码做出相应解释。我们再总结一下

这个方法的作用就是对elem身上的data缓存数据进行添加或者修正。之后的大部分操作都是集中在这个数据缓存elemData上操作。