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jQuery中数据缓存$.data的用法及源码完全解析_jquery

HTML5培训技术
一、实现原理:

对于DOM元素,通过分配一个唯一的关联id把DOM元素和该DOM元素的数据缓存对象关联起来,关联id被附加到以jQuery.expando的值命名的属性上,数据存储在全局缓存对象jQuery.cache中。在读取、设置、移除数据时,将通过关联id从全局缓存对象jQuery.cache中找到关联的数据缓存对象,然后在数据缓存对象上执行读取、设置、移除操作。

对于Javascript对象,数据则直接存储在该Javascript对象的属性jQuery.expando上。在读取、设置、移除数据时,实际上是对Javascript对象的数据缓存对象执行读取、设置、移除操作。

为了避免jQuery内部使用的数据和用户自定义的数据发生冲突,数据缓存模块把内部数据存储在数据缓存对象上,把自定义数据存储在数据缓存对象的属性data上。

二、总体结构:

// 数据缓存 DatajQuery.extend({   // 全局缓存对象   cache: {},   // 唯一 id种子   uuid:0,   // 页面中每个jQuery副本的唯一标识   expando: "jQuery" + ( jQuery.fn.jquery + Math.random() ).replace( /D/g, "" ),   // 是否有关联的数据   hasData: function(){},   // 设置、读取自定数据或内部数据   data: function(elem, name, data, pvt) {},   // 移除自定义数据或内部数据   removeData: function(elem, name, pvt) {},   // 设置、读取内部数据   _data: function(elem, name, data) {},   // 是否可以设置数据   acceptData: function(elem){}});jQuery.fn.extend({   // 设置、读取自定义数据,解析HTML5属性data-   data: function(key,value){},   // 移除自定义数据   removeData: function(key){}});// 解析HTML5属性 data-function dataAttr(elem,key,data){}// 检查数据缓存对象是否为空function isEmptyDataObject(obj){}jQuery.extend({   // 清空数据缓存对象cleanData: function(elems){}});

三、$.data(elem, name, data), $.data(elem, name)
$.data(elem, name, data)的使用方法:
如果传入参数name, data, 则设置任意类型的数据

  jQuery.data demo  <script src="//code.jquery.com/jquery-1.10.2.js?1.1.11">《script》

The values stored were and

《script》var p = $( "p" )[ 0 ];jQuery.data( p, "test", { first: 16, last: "pizza!"});$( "span:first" ).text( jQuery.data( p, "test" ).first );$( "span:last" ).text( jQuery.data( p, "test" ).last );《script》

$.data(elem, name)的使用方法:
如果传入key, 未传入参数data, 则读取并返回指定名称的数据

  jQuery.data demo  <script src="//code.jquery.com/jquery-1.10.2.js?1.1.11">《script》

A p

The "blah" value of this p is ?

《script》$( "button" ).click( function() { var value, p = $( "p" )[ 0 ]; switch ( $( "button" ).index( this ) ) { case 0 : value = jQuery.data( p, "blah" ); break; case 1 : jQuery.data( p, "blah", "hello" ); value = "Stored!"; break; case 2 : jQuery.data( p, "blah", 86 ); value = "Stored!"; break; case 3 : jQuery.removeData( p, "blah" ); value = "Removed!"; break; } $( "span" ).text( "" + value );});《script》


$.data(elem, name, data), $.data(elem, name) 源码解析:

 jQuery.extend({ // 1. 定义jQuery.data(elem, name, data, pvt) data: function( elem, name, data, pvt /* Internal Use Only */ ) {  // 2. 检查是否可以设置数据  if ( !jQuery.acceptData( elem ) ) {   return; // 如果参数elem不支持设置数据,则立即返回  }  // 3 定义局部变量  var privateCache, thisCache, ret,   internalKey = jQuery.expando,   getByName = typeof name === "string",   // 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, // elem是否是DOM元素   // 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, // 如果是DOM元素,为了避免javascript和DOM元素之间循环引用导致的浏览器(IE6/7)垃圾回收机制不起作用,要把数据存储在全局缓存对象jQuery.cache中;对于javascript对象,来及回收机制能够自动发生,不会有内存泄露的问题,因此数据可以查收存储在javascript对象上   // 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,   isEvents = name === "events";  // Avoid doing any more work than we need to when trying to get data on an  // object that has no data at all  // 4. 如果是读取数据,但没有数据,则返回  if ( (!id || !cache[id] || (!isEvents && !pvt && !cache[id].data)) && getByName && data === undefined ) {   return;   // getByName && data === undefined 如果name是字符串,data是undefined, 说明是在读取数据   // !id || !cache[id] || (!isEvents && !pvt && !cache[id].data 如果关联id不存在,说明没有数据;如果cache[id]不存在,也说明没有数据;如果是读取自动以数据,但cache[id].data不存在,说明没有自定义数据  }  // 5. 如果关联id不存在,则分配一个  if ( !id ) {   // Only DOM nodes need a new unique ID for each element since their data   // ends up in the global cache   if ( isNode ) {    elem[ internalKey ] = id = ++jQuery.uuid; // 对于DOM元素,jQuery.uuid会自动加1,并附加到DOM元素上   } else {    id = internalKey; // 对于javascript对象,关联id就是jQuery.expando   }  }  // 6. 如果数据缓存对象不存在,则初始化为空对象{}  if ( !cache[ id ] ) {   cache[ id ] = {};   // Avoids exposing jQuery metadata on plain JS objects when the object   // is serialized using JSON.stringify   if ( !isNode ) {    cache[ id ].toJSON = jQuery.noop; // 对于javascript对象,设置方法toJSON为空函数,以避免在执行JSON.stringify()时暴露缓存数据。如果一个对象定义了方法toJSON(),JSON.stringify()在序列化该对象时会调用这个方法来生成该对象的JSON元素   }  }  // An object can be passed to jQuery.data instead of a key/value pair; this gets  // shallow copied over onto the existing cache  // 7. 如果参数name是对象或函数,则批量设置数据  if ( typeof name === "object" || typeof name === "function" ) {   if ( pvt ) {    cache[ id ] = jQuery.extend( cache[ id ], name ); // 对于内部数据,把参数name中的属性合并到cache[id]中   } else {    cache[ id ].data = jQuery.extend( cache[ id ].data, name ); // 对于自定义数据,把参数name中的属性合并到cache[id].data中   }  }  // 8. 如果参数data不是undefined, 则设置单个数据  privateCache = 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 ) {   thisCache[ jQuery.camelCase( name ) ] = data;  }  // Users should not attempt to inspect the internal events object using jQuery.data,  // it is undocumented and subject to change. But does anyone listen? No.  // 9. 特殊处理events   if ( isEvents && !thisCache[ name ] ) { // 如果参数name是字符串"events",并且未设置过自定义数据"events",则返回事件婚车对象,在其中存储了事件监听函数。   return privateCache.events;  }  // Check for both converted-to-camel and non-converted data property names  // If a data property was specified  //10. 如果参数name是字符串,则读取单个数据  if ( getByName ) {   // First Try to find as-is property data   ret = thisCache[ name ]; // 先尝试读取参数name对应的数据   // Test for null|undefined property data   if ( ret == null ) { // 如果未取到,则把参数name转换为驼峰式再次尝试读取对应的数据    // Try to find the camelCased property    ret = thisCache[ jQuery.camelCase( name ) ];   }  } else { // 11. 如果未传入参数name,data,则返回数据缓存对象   ret = thisCache;  }  return ret; }, // For internal use only. _data: function( elem, name, data ) {  return jQuery.data( elem, name, data, true ); },});

四、.data(key, value), .data(key)
使用方法:

  $( "body" ).data( "foo", 52 ); // 传入key, value  $( "body" ).data( "bar", { myType: "test", count: 40 } ); // 传入key, value  $( "body" ).data( { baz: [ 1, 2, 3 ] } ); // 传入key, value  $( "body" ).data( "foo" ); // 52 // 传入key  $( "body" ).data(); // 未传入参数

HTML5 data attriubutes:

  

$( "p" ).data( "role" ) === "page"; $( "p" ).data( "lastValue" ) === 43; $( "p" ).data( "hidden" ) === true; $( "p" ).data( "options" ).name === "John";

.data(key, value), .data(key) 源码解析

jQuery.fn.extend({ // 1. 定义.data(key, value) data: function( key, value ) {  var parts, attr, name,   data = null;  // 2. 未传入参数的情况  if ( typeof key === "undefined" ) {   if ( this.length ) { // 如果参数key是undefined, 即参数格式是.data(), 则调用方法jQuery.data(elem, name, data, pvt)获取第一个匹配元素关联的自定义数据缓存对象,并返回。    data = jQuery.data( this[0] );    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], name, 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, name, data,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, 即参数格式是.data(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], key, 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, value),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, key, value );    self.triggerHandler( "changeData" + parts[1] + "!", args );   });  } }, removeData: function( key ) {  return this.each(function() {   jQuery.removeData( this, key );  }); }});// 6. 函数dataAttr(elem, key, data)解析HTML5属性data-function dataAttr( elem, key, 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, key, data );  } else {   data = undefined;  } } return data;}

五、$.removeData(elem, name),.removeData(key)
使用方法:

  jQuery.removeData demo  <script src="//code.jquery.com/jquery-1.10.2.js?1.1.11">《script》

value1 before creation:

value1 after creation:

value1 after removal:

value2 after removal:

《script》var p = $( "p" )[ 0 ];$( "span:eq(0)" ).text( "" + $( "p" ).data( "test1" ) ); //undefinedjQuery.data( p, "test1", "VALUE-1" );jQuery.data( p, "test2", "VALUE-2" );$( "span:eq(1)" ).text( "" + jQuery.data( p, "test1" ) ); // VALUE-1jQuery.removeData( p, "test1" );$( "span:eq(2)" ).text( "" + jQuery.data( p, "test1" ) ); // undefined$( "span:eq(3)" ).text( "" + jQuery.data( p, "test2" ) ); // value2《script》

  removeData demo  <script src="//code.jquery.com/jquery-1.10.2.js?1.1.11">《script》

value1 before creation:

value1 after creation:

value1 after removal:

value2 after removal:

《script》$( "span:eq(0)" ).text( "" + $( "p" ).data( "test1" ) ); // undefined$( "p" ).data( "test1", "VALUE-1" );$( "p" ).data( "test2", "VALUE-2" );$( "span:eq(1)" ).text( "" + $( "p").data( "test1" ) ); // VALUE-1$( "p" ).removeData( "test1" );$( "span:eq(2)" ).text( "" + $( "p" ).data( "test1" ) ); // undefined$( "span:eq(3)" ).text( "" + $( "p" ).data( "test2" ) ); // VALUE-2《script》

$.removeData(elem, name),.removeData(key) 源码解析:

$.extend({  // jQuery.removeData(elem,name,pvt)用于移除通过jQuery.data()设置的数据 removeData: function( elem, name, pvt /* Internal Use Only */ ) {  if ( !jQuery.acceptData( elem ) ) {   return;  }  var thisCache, i, l,   // Reference to internal data cache key   internalKey = jQuery.expando,   isNode = elem.nodeType,   // See jQuery.data for more information   cache = isNode ? jQuery.cache : elem,   // See jQuery.data for more information   id = isNode ? elem[ internalKey ] : internalKey;  // 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 emptinessfunction 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;}


六、$.hasData(elem)
使用方法:

  jQuery.hasData demo <script src="//code.jquery.com/jquery-1.10.2.js?1.1.11">《script》

Results:

《script》var $p = jQuery( "p" ), p = $p[ 0 ];$p.append( jQuery.hasData( p ) + " " ); // false$.data( p, "testing", 123 );$p.append( jQuery.hasData( p ) + " " ); // true$.removeData( p, "testing" );$p.append( jQuery.hasData( p ) + " " ); // false$p.on( "click", function() {} );$p.append( jQuery.hasData( p ) + " " ); // true$p.off( "click" );$p.append( jQuery.hasData( p ) + " " ); // false《script》$.hasData(elem) 源码解析:$.extend({ hasData: function( elem ) { elem = elem.nodeType ? jQuery.cache[ elem[jQuery.expando] ] : elem[ jQuery.expando ]; return !!elem && !isEmptyDataObject( elem ); // 如果关联的数据缓存对象存在,并且含有数据,则返回true, 否则返回false。 这里用两个逻辑非运算符! 把变量elem转换为布尔值 }});

HTML5培训技术

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