我覺得要理解off處理，得先理解on的操作，去年讀過jquery2.x的源碼，事件這塊挺複雜的。

翻看了一下自己粗糙的筆記，關於事件這塊當時講解影片沒有提及自己硬著頭皮看的。

關於綁定事件可以結合on源碼實作以及jquery.event.add方法：

我的理解是jquery主要對元素設置緩存數據cache，cache存儲了events變量(事件回調隊列集合)，以“事件”：“回調函數數組”的形式存儲，用以實現多次給某個dom添加事件時，回呼都能觸發，而實際真正用原生事件綁定的是對這個回呼函數數組的遍歷執行。

而對於off，先看看off的源碼部分：

off: function( types, selector, fn ) {
        var handleObj, type;
        if ( types && types.preventDefault && types.handleObj ) {
            // ( event )  dispatched jQuery.Event
            handleObj = types.handleObj;
            jQuery( types.delegateTarget ).off(
                handleObj.namespace ? handleObj.origType + "." + handleObj.namespace : handleObj.origType,
                handleObj.selector,
                handleObj.handler
            );
            return this;
        }
        if ( typeof types === "object" ) {
            // ( types-object [, selector] )
            for ( type in types ) {
                this.off( type, selector, types[ type ] );
            }
            return this;
        }
        if ( selector === false || typeof selector === "function" ) {
            // ( types [, fn] )
            fn = selector;
            selector = undefined;
        }
        if ( fn === false ) {
            fn = returnFalse;
        }
        return this.each(function() {
            jQuery.event.remove( this, types, fn, selector );
        });
    },

看到最後 一句，就知道，實際它呼叫了jQuery.event.remove方法。

remove方法

remove: function( elem, types, handler, selector, mappedTypes ) {

        var j, origCount, tmp,
            events, t, handleObj,
            special, handlers, type, namespaces, origType,
            elemData = data_priv.hasData( elem ) && data_priv.get( elem );

        if ( !elemData || !(events = elemData.events) ) {
            return;
        }

        // Once for each type.namespace in types; type may be omitted
        types = ( types || "" ).match( core_rnotwhite ) || [""];
        t = types.length;
        while ( t-- ) {
            tmp = rtypenamespace.exec( types[t] ) || [];
            type = origType = tmp[1];
            namespaces = ( tmp[2] || "" ).split( "." ).sort();

            // Unbind all events (on this namespace, if provided) for the element
            if ( !type ) {
                for ( type in events ) {
                    jQuery.event.remove( elem, type + types[ t ], handler, selector, true );
                }
                continue;
            }

            special = jQuery.event.special[ type ] || {};
            type = ( selector ? special.delegateType : special.bindType ) || type;
            handlers = events[ type ] || [];
            tmp = tmp[2] && new RegExp( "(^|\.)" + namespaces.join("\.(?:.*\.|)") + "(\.|$)" );

            // Remove matching events
            origCount = j = handlers.length;
            while ( j-- ) {
                handleObj = handlers[ j ];

                if ( ( mappedTypes || origType === handleObj.origType ) &&
                    ( !handler || handler.guid === handleObj.guid ) &&
                    ( !tmp || tmp.test( handleObj.namespace ) ) &&
                    ( !selector || selector === handleObj.selector || selector === "**" && handleObj.selector ) ) {
                    handlers.splice( j, 1 );

                    if ( handleObj.selector ) {
                        handlers.delegateCount--;
                    }
                    if ( special.remove ) {
                        special.remove.call( elem, handleObj );
                    }
                }
            }

            // Remove generic event handler if we removed something and no more handlers exist
            // (avoids potential for endless recursion during removal of special event handlers)
            if ( origCount && !handlers.length ) {
                if ( !special.teardown || special.teardown.call( elem, namespaces, elemData.handle ) === false ) {
                    jQuery.removeEvent( elem, type, elemData.handle );
                }

                delete events[ type ];
            }
        }

        // Remove the expando if it's no longer used
        if ( jQuery.isEmptyObject( events ) ) {
            delete elemData.handle;
            data_priv.remove( elem, "events" );
        }
    },

主要是對元素取得前面on時存放在cache的events變數對事件鍵值對進行刪除等操作。

如果只是$(xx).off('click'),那麼就是直接遍歷把events裡click事件對應的回調函數組都給刪了，如果off參數還傳了特定的回調函數，那麼則是對回呼數組遍歷比對，刪除對應的回呼函數…

對於jquery源碼這塊，前期基礎部分推薦看 妙味課堂 的視頻， 其他可以看 http://www.cnblogs.com/aaronj... 大牛博文，或者購置jquery源碼解析類似書籍。

源碼涉及的細節太多， 一時半會我也整理不出來= =，我就把大致觀點表述一下……有啥理解錯誤請指正~

以下是on的程式碼

function on( elem, types, selector, data, fn, one ) {
    var origFn, type;

    // Types can be a map of types/handlers
    if ( typeof types === "object" ) {

        // ( types-Object, selector, data )
        if ( typeof selector !== "string" ) {

            // ( types-Object, data )
            data = data || selector;
            selector = undefined;
        }
        for ( type in types ) {
            on( elem, type, selector, data, types[ type ], one );
        }
        return elem;
    }

    if ( data == null && fn == null ) {

        // ( types, fn )
        fn = selector;
        data = selector = undefined;
    } else if ( fn == null ) {
        if ( typeof selector === "string" ) {

            // ( types, selector, fn )
            fn = data;
            data = undefined;
        } else {

            // ( types, data, fn )
            fn = data;
            data = selector;
            selector = undefined;
        }
    }
    if ( fn === false ) {
        fn = returnFalse;
    } else if ( !fn ) {
        return elem;
    }

    if ( one === 1 ) {
        origFn = fn;
        fn = function( event ) {

            // Can use an empty set, since event contains the info
            jQuery().off( event );
            return origFn.apply( this, arguments );
        };

        // Use same guid so caller can remove using origFn
        fn.guid = origFn.guid || ( origFn.guid = jQuery.guid++ );
    }
    return elem.each( function() {
        jQuery.event.add( this, types, fn, data, selector );
    } );
}