$(document.body).data('aaa', 'value-aaa')console.dir(document.body)

define([ "../core", "../var/rnotwhite", "./accepts"], function( jQuery, rnotwhite ) {function Data() { // Support: Android<4, // Old WebKit does not have Object.preventExtensions/freeze method, // return new empty object instead with no [[set]] accessor Object.defineProperty( this.cache = {}, 0, { get: function() {  return {}; } }); // jQuery.expando = "jQuery" + ( version + Math.random() ).replace( //D/g, "" ) expando是一個jQuery的唯一標示 // 格式是：'jQuery//d*' 也就是'jQuery'+ 多個數字。這里為啥要搞得這么麻煩呢？ // 應因為我們可能會創建多個Data對象，為了保證每個Data對象的expando屬性的值不相等，所以這么搞 this.expando = jQuery.expando + Math.random();}Data.uid = 1; // Data函數的屬性，'靜態屬性'Data.accepts = jQuery.acceptData;Data.prototype = { key: function( owner ) { // We can accept data for non-element nodes in modern browsers, // but we should not, see #8335. // Always return the key for a frozen object. // 若owner在該緩存池中存在對應的緩存對象，則返回混存對象的key(是一個數字)， // 若owner在該緩存池中不存在對應的緩存對象，則在緩存池中為其創建一個緩存對象，并返回該緩存對象的key if ( !Data.accepts( owner ) ) {  return 0; } var descriptor = {},  // Check if the owner object already has a cache key  // 檢查owner對象在該緩存池中是否存在緩存  unlock = owner[ this.expando ]; // 是一個數字，用來作為緩存池中緩存對象的key // If not, create one // 如果沒有，則創建一個 if ( !unlock ) {  unlock = Data.uid++;  // Secure it in a non-enumerable, non-writable property  // 給owner附加一個屬性 owner[this.expando] = unlock ，并且該屬性不能被枚舉，  try {  descriptor[ this.expando ] = { value: unlock };  Object.defineProperties( owner, descriptor );  // Support: Android<4  // Fallback to a less secure definition  } catch ( e ) {  descriptor[ this.expando ] = unlock;  jQuery.extend( owner, descriptor );  } } // Ensure the cache object // 確保owner對應的緩存對象已存在 if ( !this.cache[ unlock ] ) {  this.cache[ unlock ] = {}; } // 返回unlock return unlock; }, set: function( owner, data, value ) { // 設置owner對應的緩存對象 var prop,  // There may be an unlock assigned to this node,  // if there is no entry for this "owner", create one inline  // and set the unlock as though an owner entry had always existed  unlock = this.key( owner ), // 獲取owner的對應的緩存對象在緩存池中的key(這里的key，是鍵值對中的鍵的意思)  cache = this.cache[ unlock ]; // 獲取owner所對應的緩存對象 // Handle: [ owner, key, value ] args // 根據傳入參數的個數以及類型實現重載 if ( typeof data === "string" ) {  cache[ data ] = value; // Handle: [ owner, { properties } ] args } else {  // Fresh assignments by object are shallow copied  if ( jQuery.isEmptyObject( cache ) ) {  jQuery.extend( this.cache[ unlock ], data );  // Otherwise, copy the properties one-by-one to the cache object  } else {  for ( prop in data ) {   cache[ prop ] = data[ prop ];  }  } } // 返回緩存對象 return cache; }, get: function( owner, key ) { // 獲取owner對象的名為key的屬性值 // owner:是一個對象(可以是jQuery對象也可以是DOM對象) key: 屬性名 // Either a valid cache is found, or will be created. // New caches will be created and the unlock returned, // allowing direct access to the newly created // empty data object. A valid owner object must be provided. var cache = this.cache[ this.key( owner ) ]; // owner的緩存對象 return key === undefined ? cache : cache[ key ]; // 沒指定key的話就返回整個緩存對象，若指定了key則返回在該緩存對象的key屬性的值 }, access: function( owner, key, value ) { var stored; // In cases where either: // // 1. No key was specified 沒有指定key // 2. A string key was specified, but no value provided 指定了字符串格式的key，但沒有指定value // // Take the "read" path and allow the get method to determine // which value to return, respectively either: // // 1. The entire cache object 整個緩存對象 // 2. The data stored at the key 緩存對象中某個鍵的值 // if ( key === undefined || // 沒有指定key或者指定了字符串格式的key，但沒有指定value  ((key && typeof key === "string") && value === undefined) ) {  // 沒有指定key：獲取整個緩存對象  // 指定了字符串格式的key，但沒有指定value： 獲取緩存對象中key的值  stored = this.get( owner, key );  return stored !== undefined ?  stored : this.get( owner, jQuery.camelCase(key) ); } // [*]When the key is not a string, or both a key and value // are specified, set or extend (existing objects) with either: // 當key不是一個字符串，或者key和value都指定了，就會根據情況進行設置或者擴展 // // 1. An object of properties // 2. A key and value // this.set( owner, key, value ); // Since the "set" path can have two possible entry points // return the expected data based on which path was taken[*] return value !== undefined ? value : key; }, remove: function( owner, key ) { // 清空owner對應的緩存對象，或者移除緩存對象中的某個鍵值對 var i, name, camel,  unlock = this.key( owner ),  cache = this.cache[ unlock ]; // 如果沒有指定key，則清空緩存對象 if ( key === undefined ) {  this.cache[ unlock ] = {}; } else {  // Support array or space separated string of keys  if ( jQuery.isArray( key ) ) {  // 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 = key.concat( key.map( jQuery.camelCase ) );  } else {  camel = jQuery.camelCase( key );  // Try the string as a key before any manipulation  if ( key in cache ) {   name = [ key, camel ];  } else {   // If a key with the spaces exists, use it.   // Otherwise, create an array by matching non-whitespace   name = camel;   name = name in cache ?   [ name ] : ( name.match( rnotwhite ) || [] );  }  }  i = name.length;  while ( i-- ) {  delete cache[ name[ i ] ];  } } }, hasData: function( owner ) { // 檢查owner在該緩存池中是否存在緩存對象 return !jQuery.isEmptyObject(  this.cache[ owner[ this.expando ] ] || {} ); }, discard: function( owner ) { if ( owner[ this.expando ] ) {  delete this.cache[ owner[ this.expando ] ]; } }};return Data;});

jQuery.extend({ hasData: function( elem ) { return dataUser.hasData( elem ) || dataPriv.hasData( elem ); }, data: function( elem, name, data ) { return dataUser.access( elem, name, data ); }, removeData: function( elem, name ) { dataUser.remove( elem, name ); }, // TODO: Now that all calls to _data and _removeData have been replaced // with direct calls to dataPriv methods, these can be deprecated. _data: function( elem, name, data ) { return dataPriv.access( elem, name, data ); }, _removeData: function( elem, name ) { dataPriv.remove( elem, name ); }});

jQuery.fn.extend({ data: function( key, value ) { var i, name, data,  elem = this[ 0 ],  attrs = elem && elem.attributes;return access( this, function( value ) {  var data,  camelKey = jQuery.camelCase( key );// 從這里可以看出，為jQuery對象中的每個DOM元素分別附加數據  this.each(function() {  // First, attempt to store a copy or reference of any  // data that might've been store with a camelCased key.  var data = dataUser.get( this, camelKey );  // For HTML5 data-* attribute interop, we have to  // store property names with dashes in a camelCase form.  // This might not apply to all properties...*  dataUser.set( this, camelKey, value );  // *... In the case of properties that might _actually_  // have dashes, we need to also store a copy of that  // unchanged property.  if ( key.indexOf("-") !== -1 && data !== undefined ) {   dataUser.set( this, key, value );  }  }); }, null, value, arguments.length > 1, null, true ); }, removeData: function( key ) { return this.each(function() {  dataUser.remove( this, key ); }); }});