读jQuery源码 jQuery.data

var rbrace = /(?:\{[\s\S]*\}|\[[\s\S]*\])$/,
    rmultiDash = /([A-Z])/g;

function internalData( elem, name, data, pvt /* Internal Use Only */ ){

    //如果elem元素不能附加值，退出
    if ( !jQuery.acceptData( elem ) ) {
        return;
    }

    // ## form core.js
    // Unique for each copy of jQuery on the page
    // Non-digits removed to match rinlinejQuery
    // expando: "jQuery" + ( core_version + Math.random() ).replace( /\D/g, "" ),
    // 每个Jquery都有单独的一个expando

    var ret, thisCache,
        internalKey = jQuery.expando,

        // We have to handle DOM nodes and JS objects differently because IE6-7
        // can't GC object references properly across the DOM-JS boundary
        // 由于IE6,7不能自动回收再DOM上的引用，所以要对DOM和JS对象区别对待
        isNode = elem.nodeType,

        // Only DOM nodes need the global jQuery cache; JS object data is
        // attached directly to the object so GC can occur automatically
        // 只有DOM需要全局的缓存变量，对象就直接插入值了
        cache = isNode ? jQuery.cache : elem,

        // Only defining an ID for JS objects if its cache already exists allows
        // the code to shortcut on the same path as a DOM node with no cache
        id = isNode ? elem[ internalKey ] : elem[ internalKey ] && internalKey;

        // 什么时候会出现id为undefined的时候？
        // internalData(document.createElement('div'),'namea',...)
        // internalData({});

    // Avoid doing any more work than we need to when trying to get data on an
    // object that has no data at all
    if ( (!id || !cache[id] || (!pvt && !cache[id].data)) && data === undefined && typeof name === "string" ) {
        return;
    }

    // 如果有name而没有data，说明这是一个读取的动作
    // 但是没有得到id，获取cache[id]中啥都没有，在获取用户数据的时候cache[id].data啥都木有，就返回空

    if ( !id ) {
        // Only DOM nodes need a new unique ID for each element since their data
        // ends up in the global cache
        // 如果是DOM元素，则取得一个唯一的ID值
        if ( isNode ) {
            id = elem[ internalKey ] = core_deletedIds.pop() || jQuery.guid++;
        } else {
            id = internalKey; //这是jQuery.expando
        }
    }

    if ( !cache[ id ] ) {
        // Avoid exposing jQuery metadata on plain JS objects when the object
        // is serialized using JSON.stringify
        // 避免只用JSON.stringify(cache[id]) 所带来的循环引用
        cache[ id ] = isNode ? {} : { toJSON: jQuery.noop };
    }

    // An object can be passed to jQuery.data instead of a key/value pair; this gets
    // shallow copied over onto the existing cache
    // 也可以穿一个jQuery.data，浅拷贝过来

    // jQuery.data({},{name:'hhstuhacker',age:31})
    // cache[id] = {data:{name:'hhstuhacker',age:31}};

    // cache[ id ]存入的是jQuery的内部数据
    // cache[ id ].data 存入的是用户数据
    // 若果pvt为真，就拷贝到cache[ id ]里
    // 若果pvt为false，就拷贝到cache[ id ].data 里

    if ( typeof name === "object" || typeof name === "function" ) {
        if ( pvt ) {
            cache[ id ] = jQuery.extend( cache[ id ], name ); //直接拷贝，内部使用
        } else {
            cache[ id ].data = jQuery.extend( cache[ id ].data, name ); //直接拷贝data
        }
    }

    thisCache = cache[ id ];

    // jQuery data() is stored in a separate object inside the object's internal data
    // cache in order to avoid key collisions between internal data and user-defined
    // data.

    // jQuery.cache = {jQuery.expando: {data:{}}};
    // 这里是为了防止内部数据跟用户定义的数据项混淆，内部数据定义在jQ.cache里，用户定义数据在jQ.cache.[id] 里

    if ( !pvt ) {
        if ( !thisCache.data ) {
            thisCache.data = {};
        }

        thisCache = thisCache.data;
    }

    // 分情况了，如果传入了键值对，就设置之
    // 将camelCase驼峰
    if ( data !== undefined ) {
        thisCache[ jQuery.camelCase( name ) ] = data;
    }

    // Check for both converted-to-camel and non-converted data property names
    // If a data property was specified
    // 不管是否读取还是设置缓存，都会返回数据
    // 先尝试直接获取，如果获取不成功，就尝试驼峰式获取
    // 如果连name都没有指定，就获取整个thisCache对象
    if ( typeof name === "string" ) {

        // First Try to find as-is property data
        ret = thisCache[ name ];

        // Test for null|undefined property data
        if ( ret == null ) {

            // Try to find the camelCased property
            ret = thisCache[ jQuery.camelCase( name ) ];
        }
    } else {
        ret = thisCache;
    }

    return ret;
}

function internalRemoveData( elem, name, pvt ) {
    if ( !jQuery.acceptData( elem ) ) { //如果elem元素不能附加值，退出
        return;
    }

    var thisCache, i,
        isNode = elem.nodeType,

        // See jQuery.data for more information
        cache = isNode ? jQuery.cache : elem,
        id = isNode ? elem[ jQuery.expando ] : jQuery.expando;

    // If there is already no cache entry for this object, there is no
    // purpose in continuing
    // 如果没有得到cache[ id ] 那就不进行了
    if ( !cache[ id ] ) {
        return;
    }

    if ( name ) {

        thisCache = pvt ? cache[ id ] : cache[ id ].data;

        if ( thisCache ) {

            // Support array or space separated string names for data keys
            // $.removeData(element,['title','age','createTime']);
            // $.removeData(element,'title age createTime');
            if ( !jQuery.isArray( name ) ) {

                // try the string as a key before any manipulation
                if ( name in thisCache ) {
                    name = [ name ];
                } else {

                    // split the camel cased version by spaces unless a key with the spaces exists
                    // 检测是否驼峰式在其中，如果不在，将其split
                    name = jQuery.camelCase( name );
                    if ( name in thisCache ) {
                        name = [ name ];
                    } else {
                        name = name.split(" ");
                    }
                }
            } else {
                // If "name" is an array of keys...
                // When data is initially created, via ("key", "val") signature,
                // keys will be converted to camelCase.
                // Since there is no way to tell _how_ a key was added, remove
                // both plain key and camelCase key. #12786
                // This will only penalize the array argument path.
                name = name.concat( jQuery.map( name, jQuery.camelCase ) );

                // 将不驼峰和驼峰的全部删除
            }

            //删除之
            i = name.length;
            while ( i-- ) {
                delete thisCache[ name[i] ];
            }

            // If there is no data left in the cache, we want to continue
            // and let the cache object itself get destroyed

            // 如果说删除过后，cache[id]或者cache[id].data 都是空了，那么咱们需要清理下一步吧？
            if ( pvt ? !isEmptyDataObject(thisCache) : !jQuery.isEmptyObject(thisCache) ) {
                return;
            }
        }
    }

    // See jQuery.data for more information
    // 如果是用户使用的话，清空cache[id].data
    // 如果cache [ id ] 不是空的话，结束该函数
    // 如果cahce [ id ] 是空的话，还是下一步的清理行动啊
    if ( !pvt ) {
        delete cache[ id ].data;

        // Don't destroy the parent cache unless the internal data object
        // had been the only thing left in it
        if ( !isEmptyDataObject( cache[ id ] ) ) {
            return;
        }
    }

    // window.window === window;
    // isWindow: function (o) {return o.window === window;}
    // cache != cache.window 表示不是window

    // Destroy the cache
    // 如果是个DOM节点，那么cleanData
    if ( isNode ) {
        jQuery.cleanData( [ elem ], true );

    // ses: http://www.cnblogs.com/enein/archive/2012/08/23/2651312.html
    // Use delete when supported for expandos or `cache` is not a window per isWindow (#10080)
    // 经测试，在IE6,7,8下面，var div = document.createElement('div') delete div.test;
    // 是报错的 而 jQuery.support.deleteExpando 正是这种检测
    } else if ( jQuery.support.deleteExpando || cache != cache.window ) {
        delete cache[ id ];

    // When all else fails, null
    } else {
        cache[ id ] = null;
    }
}

jQuery.extend({
    cache: {},

    // The following elements throw uncatchable exceptions if you
    // attempt to add expando properties to them.
    // 这几个元素不能有附加值
    noData: {
        "applet": true,
        "embed": true,
        // Ban all objects except for Flash (which handle expandos)
        "object": "clsid:D27CDB6E-AE6D-11cf-96B8-444553540000"
    },

    hasData: function( elem ) {
        elem = elem.nodeType ? jQuery.cache[ elem[jQuery.expando] ] : elem[ jQuery.expando ];
        return !!elem && !isEmptyDataObject( elem );
    },

    data: function( elem, name, data ) {
        return internalData( elem, name, data );
    },

    removeData: function( elem, name ) {
        return internalRemoveData( elem, name );
    },

    // For internal use only.
    // 内部适用，这里设置pvt为true，返回内部数据，定位到cache[id]这一层
    _data: function( elem, name, data ) {
        return internalData( elem, name, data, true );
    },

    // 内部适用，这里设置pvt为true，返回内部数据，定位到cache[id]这一层
    _removeData: function( elem, name ) {
        return internalRemoveData( elem, name, true );
    },

    // A method for determining if a DOM node can handle the data expando
    acceptData: function( elem ) {
        // Do not set data on non-element because it will not be cleared (#8335).
        // 如果是个dom节点，并且不是element也不是document，那就表示不能被附加数据
        // see:http://www.cnblogs.com/hhstuhacker/p/NodeType.html
        if ( elem.nodeType && elem.nodeType !== 1 && elem.nodeType !== 9 ) {
            return false;
        }

        var noData = elem.nodeName && jQuery.noData[ elem.nodeName.toLowerCase() ];

        // nodes accept data unless otherwise specified; rejection can be conditional
        // 如果是embed或者applet，或者是flash元素，就返回false
        // about falsh:: http://www.w3help.org/zh-cn/causes/HO8001
        return !noData || noData !== true && elem.getAttribute("classid") === noData;
    }
});

jQuery.fn.extend({
    data: function( key, value ) {
        var attrs, name,
            data = null,
            i = 0,
            elem = this[0];

        // Special expections of .data basically thwart jQuery.access,
        // so implement the relevant behavior ourselves

        // Gets all values
        // 如果key为undefined，那就表示要取得所有的data
        if ( key === undefined ) {
            if ( this.length ) {
                data = jQuery.data( elem ); //默认取第一个

                // 看看cache内部是否已经解析过该DOM了，parsedAttrs
                // 如果没有，得到属性列表

                if ( elem.nodeType === 1 && !jQuery._data( elem, "parsedAttrs" ) ) {
                    attrs = elem.attributes;
                    for ( ; i < attrs.length; i++ ) {
                        name = attrs[i].name;

                        if ( name.indexOf("data-") === 0 ) {
                            name = jQuery.camelCase( name.slice(5) );

                            //这里的data[ name ]为空值
                            dataAttr( elem, name, data[ name ] );
                        }
                    }

                    //标记已经解析过了
                    jQuery._data( elem, "parsedAttrs", true );
                }
            }

            return data;
        }

        // Sets multiple values
        // 如果是个对象，递归调用之
        if ( typeof key === "object" ) {
            return this.each(function() {
                jQuery.data( this, key );
            });
        }

        return arguments.length > 1 ?

            // Sets one value
            this.each(function() {
                jQuery.data( this, key, value );
            }) :

            //$('.color-box').data('someone','new');

            // Gets one value
            // Try to fetch any internally stored data first
            elem ? dataAttr( elem, key, jQuery.data( elem, key ) ) : null;

            //$('#box').data('dataFirst');

            // <div data-data-first="something....."></div>
    },

    removeData: function( key ) {
        return this.each(function() {
            jQuery.removeData( this, key );
        });
    }
});

function dataAttr( elem, key, data ) {
    // If nothing was found internally, try to fetch any
    // data from the HTML5 data-* attribute
    //这个函数，主要是处理HTML5的问题
    if ( data === undefined && elem.nodeType === 1 ) {

        // 驼峰反转
        var name = "data-" + key.replace( rmultiDash, "-$1" ).toLowerCase();

        data = elem.getAttribute( name );

        // rbrace 对象或者数组正则

        if ( typeof data === "string" ) {
            try {
                data = data === "true" ? true :
                    data === "false" ? false :
                    data === "null" ? null :
                    // Only convert to a number if it doesn't change the string
                    +data + "" === data ? +data :
                    rbrace.test( data ) ? jQuery.parseJSON( data ) :
                        data;
            } catch( e ) {}

            // Make sure we set the data so it isn't changed later
            jQuery.data( elem, key, data );

            //设置进去

        } else {
            data = undefined;
        }
    }

    return data;
}

// checks a cache object for emptiness
function isEmptyDataObject( obj ) {
    var name;
    for ( name in obj ) {

        // if the public data object is empty, the private is still empty
        // 如果cache.data 为空，跳过本次循环，不判断了
        // 如果不跳过啊，就走到下面了吧，name !== data 杠杠的
        if ( name === "data" && jQuery.isEmptyObject( obj[name] ) ) {
            continue;
        }

        //toJSON是内置的，如果看到其他name，就不为空
        if ( name !== "toJSON" ) {
            return false;
        }
    }

    return true;
}

jQuery的版本为1.9.2