if ( this[0].nodeType === 1 && !jQuery._data( this[0],"parsedAttrs" ) ) {
 attr = this[0].attributes;
 for ( var i = 0,l = attr.length; i < l; i++ ) {
  name = attr[i].name;

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

   dataAttr( this[0],data[ name ] );
  }
 }
 jQuery._data( this[0],"parsedAttrs",true );
}

}

return data;
// 3. 参数key 是对象的情况,即参数格式是.data(key),则遍历匹配元素集合，为每个匹配元素调用方法jQuery.data(elem,pvt)批量设置数据
} else if ( typeof key === "object" ) {
return this.each(function() {
jQuery.data( this,key );
});
}
// 4. 只传入参数key的情况 如果只传入参数key,则返回第一个匹配元素的指定名称数据
parts = key.split(".");
parts[1] = parts[1] ? "." + parts[1] : "";

if ( value === undefined ) {
data = this.triggerHandler("getData" + parts[1] + "!",[parts[0]]);

// Try to fetch any internally stored data first
if ( data === undefined && this.length ) {
data = jQuery.data( this[0],key );
data = dataAttr( this[0],data );
}

return data === undefined && parts[1] ?
this.data( parts[0] ) :
data;

// 5. 传入参数key和value的情况 即参数格式是.data(key,则为每个匹配元素设置任意类型的数据，并触发自定义事件setData,changeData
} else {
return this.each(function() {
var self = jQuery( this ),args = [ parts[0],value ];

self.triggerHandler( "setData" + parts[1] + "!",args );
jQuery.data( this,value );
self.triggerHandler( "changeData" + parts[1] + "!",args );

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

// 6. 函数dataAttr(elem,data)解析HTML5属性data-
function dataAttr( elem,data ) {
// If nothing was found internally,try to fetch any
// data from the HTML5 data-* attribute
// 只有参数data为undefined时，才会解析HTML5属性data-
if ( data === undefined && elem.nodeType === 1 ) {

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

data = elem.getAttribute( name );

if ( typeof data === "string" ) {
try {
data = data === "true" ? true :
data === "false" ? false :
data === "null" ? null :
jQuery.isNumeric( data ) ? parseFloat( 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,data );

} else {
data = undefined;
}
}

return data;
}

// If there is already no cache entry for this object,there is no
// purpose in continuing
if ( !cache[ id ] ) {
return;
}

// 如果传入参数name,则移除一个或多个数据

if ( name ) {

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

if ( thisCache ) { // 只有数据缓存对象thisCache存在时，才有必要移除数据

// Support array or space separated string names for data keys
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
  name = jQuery.camelCase( name );
  if ( name in thisCache ) {
   name = [ name ];
  } else {
   name = name.split( " " );
  }
 }
}

// 遍历参数name中的数据名，用运算符delete逐个从数据缓存对象thisCache中移除
for ( i = 0,l = name.length; i < l; 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
if ( !( pvt ? isEmptyDataObject : jQuery.isEmptyObject )( thisCache ) ) {
 return;
}

}
}

// See jQuery.data for more information
// 删除自定义数据缓存对象cache[id].data
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;
}
}

// Browsers that fail expando deletion also refuse to delete expandos on
// the window,but it will allow it on all other JS objects; other browsers
// don't care
// Ensure that cache is not a window object #10080
// 删除数据缓存对象cache[id]
if ( jQuery.support.deleteExpando || !cache.setInterval ) {
delete cache[ id ];
} else {
cache[ id ] = null;
}

// We destroyed the cache and need to eliminate the expando on the node to avoid
// false lookups in the cache for entries that no longer exist
// 删除DOM元素上扩展的jQuery.expando属性
if ( isNode ) {
// IE does not allow us to delete expando properties from nodes,// nor does it have a removeAttribute function on Document nodes;
// we must handle all of these cases
if ( jQuery.support.deleteExpando ) {
delete elem[ internalKey ];
} else if ( elem.removeAttribute ) {
elem.removeAttribute( internalKey );
} else {
elem[ internalKey ] = null;
}
}
}
});

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

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

// if the public data object is empty,the private is still empty
if ( name === "data" && jQuery.isEmptyObject( obj[name] ) ) {
continue;
}
if ( name !== "toJSON" ) {
return false;
}
}

return true;
}