jQuery数据缓存$.data 的使用以及源码解析

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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

<!doctype html><html lang="en"><head>  <meta charset="utf-8">  <title>jQuery.data demo</title>  <style>  div {    color: blue;  }  span {    color: red;  }  </style>  <script src="//code.jquery.com/jquery-1.10.2.js"></script></head><body><div>  The values stored were  <span></span>  and  <span></span></div><script>var div = $( "div" )[ 0 ];jQuery.data( div, "test", {  first: 16,  last: "pizza!"});$( "span:first" ).text( jQuery.data( div, "test" ).first );$( "span:last" ).text( jQuery.data( div, "test" ).last );</script></body></html>

$.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

<!doctype html><html lang="en"><head>  <meta charset="utf-8">  <title>jQuery.data demo</title>  <style>  div {    margin: 5px;    background: yellow;  }  button {    margin: 5px;    font-size: 14px;  }  p {    margin: 5px;    color: blue;  }  span {    color: red;  }  </style>  <script src="//code.jquery.com/jquery-1.10.2.js"></script></head><body><div>A div</div><button>Get "blah" from the div</button><button>Set "blah" to "hello"</button><button>Set "blah" to 86</button><button>Remove "blah" from the div</button><p>The "blah" value of this div is <span>?</span></p><script>$( "button" ).click( function() {  var value,    div = $( "div" )[ 0 ];  switch ( $( "button" ).index( this ) ) {  case 0 :    value = jQuery.data( div, "blah" );    break;  case 1 :    jQuery.data( div, "blah", "hello" );    value = "Stored!";    break;  case 2 :    jQuery.data( div, "blah", 86 );    value = "Stored!";    break;  case 3 :    jQuery.removeData( div, "blah" );    value = "Removed!";    break;  }  $( "span" ).text( "" + value );});</script></body></html>

$.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:

    <div data-role="page" data-last-value="43" data-hidden="true" data-options='{"name":"John"}'></div>    $( "div" ).data( "role" ) === "page";    $( "div" ).data( "lastValue" ) === 43;    $( "div" ).data( "hidden" ) === true;    $( "div" ).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：

<!doctype html><html lang="en"><head>  <meta charset="utf-8">  <title>jQuery.removeData demo</title>  <style>  div {    margin: 2px;    color: blue;  }  span {    color: red;  }  </style>  <script src="//code.jquery.com/jquery-1.10.2.js"></script></head><body><div>value1 before creation: <span></span></div><div>value1 after creation: <span></span></div><div>value1 after removal: <span></span></div><div>value2 after removal: <span></span></div><script>var div = $( "div" )[ 0 ];$( "span:eq(0)" ).text( "" + $( "div" ).data( "test1" ) ); //undefinedjQuery.data( div, "test1", "VALUE-1" );jQuery.data( div, "test2", "VALUE-2" );$( "span:eq(1)" ).text( "" + jQuery.data( div, "test1" ) ); // VALUE-1jQuery.removeData( div, "test1" );$( "span:eq(2)" ).text( "" + jQuery.data( div, "test1" ) ); // undefined$( "span:eq(3)" ).text( "" + jQuery.data( div, "test2" ) ); // value2</script></body></html><!doctype html><html lang="en"><head>  <meta charset="utf-8">  <title>removeData demo</title>  <style>  div {    margin: 2px;    color: blue;  }  span {    color: red;  }  </style>  <script src="//code.jquery.com/jquery-1.10.2.js"></script></head><body><div>value1 before creation: <span></span></div><div>value1 after creation: <span></span></div><div>value1 after removal: <span></span></div><div>value2 after removal: <span></span></div><script>$( "span:eq(0)" ).text( "" + $( "div" ).data( "test1" ) ); // undefined$( "div" ).data( "test1", "VALUE-1" );$( "div" ).data( "test2", "VALUE-2" );$( "span:eq(1)" ).text( "" + $( "div").data( "test1" ) ); // VALUE-1$( "div" ).removeData( "test1" );$( "span:eq(2)" ).text( "" + $( "div" ).data( "test1" ) ); // undefined$( "span:eq(3)" ).text( "" + $( "div" ).data( "test2" ) ); // VALUE-2</script></body></html>

$.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：

<!doctype html><html lang="en"><head>  <meta charset="utf-8">  <title>jQuery.hasData demo</title>  <script src="//code.jquery.com/jquery-1.10.2.js"></script></head><body><p>Results: </p><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></body></html>

$.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  }});

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