var a=new Object;

var b=new Object;

a.r=b;

b.r=a;

var a=new Object;

a.r=a;

{ "uid1": { // DOM节点1缓存数据，
        "name1": value1,
        "name2": value2
    },
    "uid2": { // DOM节点2缓存数据，
        "name1": value1,
        "name2": value2
    }

var obj = {};
$.data(obj , "a" , 1);//普通对象添加数据
console.log($.data(obj,"a"));//1
var dom = $("body");//dom添加数据
$.data(dom,"a",1)
console.log($.data(dom,"a"));//1
$.data(obj , {"b":2});//两个参数 绑定数据对象
console.log($.data(dom,"b"));//2
console.log($.data(dom));//1 2

$("body").data("a" , 1);//添加数据
console.log($("body").data("a"));//1
$("body").data({"b":2});//两个参数 绑定数据对象
console.log($("body").data("b"));//2
console.log($("body").data();//1 2

$.data($("body")[0],{"a":1});
console.log($.data($("body")[0],"a"));

expando: "jQuery" + ( jQuery.fn.jquery + Math.random() ).replace( /\D/g, "" )

function internalData( elem, name, data, pvt /* Internal Use Only */ ){
    if ( !jQuery.acceptData( elem ) ) {//查看是否可以接受数据
        return;
    }
    var ret, thisCache,
        internalKey = jQuery.expando,//jQuery副本的唯一标识
        // We have to handle DOM nodes and JS objects differently because IE6-7
        // can‘t GC object references properly across the DOM-JS boundary
        isNode = elem.nodeType,//判断DOM节点
        // Only DOM nodes need the global jQuery cache; JS object data is
        // attached directly to the object so GC can occur automatically
        cache = isNode ? jQuery.cache : elem,//若是是DOM对象，则cache就是$.cache,否则为参数elem对象
        // 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;//找id，id可能在DOM[expando]中，也可以在elem[expando]中
    // 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;//参数的一些判断限制
    }
    if ( !id ) {//id不存在
        // Only DOM nodes need a new unique ID for each element since their data
        // ends up in the global cache
        if ( isNode ) {//是DOM节点
            id = elem[ internalKey ] = core_deletedIds.pop() || jQuery.guid++;//生成一个id
        } else {//不是DOM，是一个对象
            id = internalKey;//那么id就是那个expando
        }
    }
    if ( !cache[ id ] ) {//cache中不存在数据，先弄成空的，一会在填充
        // Avoid exposing jQuery metadata on plain JS objects when the object
        // is serialized using JSON.stringify
        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
    if ( typeof name === "object" || typeof name === "function" ) {//处理第二个参数时对象或者是函数的情况
        if ( pvt ) {//不太懂
            cache[ id ] = jQuery.extend( cache[ id ], name );
        } else {//添加到data属性上
            cache[ id ].data = jQuery.extend( cache[ id ].data, name );
        }
    }
    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.
    if ( !pvt ) {
        if ( !thisCache.data ) {
            thisCache.data = {};
        }
        thisCache = thisCache.data;
    }
    if ( data !== undefined ) {//第三个参数存在，就是存数据
        thisCache[ jQuery.camelCase( name ) ] = data;
    }
    // Check for both converted-to-camel and non-converted data property names
    // If a data property was specified
    if ( typeof name === "string" ) {

        // First Try to find as-is property data
        ret = thisCache[ name ];//取出来待返回的那个value
                //有啥用 这么麻烦
        // Test for null|undefined property data
        if ( ret == null ) {
            // Try to find the camelCased property
            ret = thisCache[ jQuery.camelCase( name ) ];
        }
    } else {
        ret = thisCache;//就是返回存进来的那个对象或者函数
    }
    return ret; 
}

var obj = {};
$.data(obj,{"a":1});
console.log($.data(obj,"a"));
console.log(obj);

        var a = $("body");
        var b = $("body");
        a.data("a",1);
        b.data("a",2);
        console.log(a.data("a"));//2
        console.log(b.data("a"));//2

        $.data(a,"b",1);
        $.data(b,"b",2);
        console.log($.data(a,"b"))//1
        console.log($.data(b,"b"))//2

        $.data(a[0],"b",1);
        $.data(b[0],"b",2);
        console.log($.data(a[0],"b"));//2
        console.log($.data(b[0],"b"));//2

var a = $("body");
var b = $("body");
console.log(a[0] == b[0]);//true
console.log(a == b);//false
console.log( $("body") == $("body"));//false

        var a = $("body");
        var b = $("body");
        a.data("a",1);
        b.data("a",2);
        console.log(a.data("a"));//2
        console.log(b.data("a"));//2

this.each(function() {
                jQuery.data( this, key, value );
            })