深入学习jQuery中的data()

$(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是一个jQuery的唯一标示
 // 格式是：'jQuery\\d*' 也就是'jQuery'+ 多个数字。这里为啥要搞得这么麻烦呢？
 // 应因为我们可能会创建多个Data对象，为了保证每个Data对象的expando属性的值不相等，所以这么搞
 this.expando = jQuery.expando + Math.random();
}

Data.uid = 1; // Data函数的属性，'静态属性'
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在该缓存池中存在对应的缓存对象，则返回混存对象的key(是一个数字)，
 // 若owner在该缓存池中不存在对应的缓存对象，则在缓存池中为其创建一个缓存对象，并返回该缓存对象的key
 if ( !Data.accepts( owner ) ) {
  return 0;
 }

 var descriptor = {},
  // Check if the owner object already has a cache key
  // 检查owner对象在该缓存池中是否存在缓存
  unlock = owner[ this.expando ]; // 是一个数字，用来作为缓存池中缓存对象的key

 // If not, create one
 // 如果没有，则创建一个
 if ( !unlock ) {
  unlock = Data.uid++;

  // Secure it in a non-enumerable, non-writable property
  // 给owner附加一个属性 owner[this.expando] = unlock ，并且该属性不能被枚举，
  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
 // 确保owner对应的缓存对象已存在
 if ( !this.cache[ unlock ] ) {
  this.cache[ unlock ] = {};
 }
 // 返回unlock
 return unlock;
 },
 set: function( owner, data, value ) {
 // 设置owner对应的缓存对象
 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 ), // 获取owner的对应的缓存对象在缓存池中的key(这里的key，是键值对中的键的意思)
  cache = this.cache[ unlock ]; // 获取owner所对应的缓存对象

 // Handle: [ owner, key, value ] args
 // 根据传入参数的个数以及类型实现重载
 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 ];
  }
  }
 }
 // 返回缓存对象
 return cache;
 },
 get: function( owner, key ) {
 // 获取owner对象的名为key的属性值
 // owner:是一个对象(可以是jQuery对象也可以是DOM对象) key: 属性名
 // 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的缓存对象

 return key === undefined ? cache : cache[ key ]; // 没指定key的话就返回整个缓存对象，若指定了key则返回在该缓存对象的key属性的值
 },
 access: function( owner, key, value ) {
 var stored;
 // In cases where either:
 //
 // 1. No key was specified 没有指定key
 // 2. A string key was specified, but no value provided 指定了字符串格式的key，但没有指定value
 //
 // Take the "read" path and allow the get method to determine
 // which value to return, respectively either:
 //
 // 1. The entire cache object 整个缓存对象
 // 2. The data stored at the key 缓存对象中某个键的值
 //
 if ( key === undefined || // 没有指定key或者指定了字符串格式的key，但没有指定value
  ((key && typeof key === "string") && value === undefined) ) {

  // 没有指定key：获取整个缓存对象
  // 指定了字符串格式的key，但没有指定value： 获取缓存对象中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:
 // 当key不是一个字符串，或者key和value都指定了，就会根据情况进行设置或者扩展
 //
 // 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对应的缓存对象，或者移除缓存对象中的某个键值对
 var i, name, camel,
  unlock = this.key( owner ),
  cache = this.cache[ unlock ];
 // 如果没有指定key，则清空缓存对象
 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 ) {
 // 检查owner在该缓存池中是否存在缓存对象
 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 );

// 从这里可以看出，为jQuery对象中的每个DOM元素分别附加数据
  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 );
 });
 }
});