一、實現原理：
對于DOM元素，通過分配一個唯一的關聯id把DOM元素和該DOM元素的數據緩存對象關聯起來，關聯id被附加到以jQuery.expando的值命名的屬性上，數據存儲在全局緩存對象jQuery.cache中。在讀取、設置、移除數據時，將通過關聯id從全局緩存對象jQuery.cache中找到關聯的數據緩存對象，然后在數據緩存對象上執行讀取、設置、移除操作。
對于Javascript對象，數據則直接存儲在該Javascript對象的屬性jQuery.expando上。在讀取、設置、移除數據時，實際上是對Javascript對象的數據緩存對象執行讀取、設置、移除操作。
為了避免jQuery內部使用的數據和用戶自定義的數據發生沖突，數據緩存模塊把內部數據存儲在數據緩存對象上，把自定義數據存儲在數據緩存對象的屬性data上。
二、總體結構：
// 數據緩存 DatajQuery.extend({ // 全局緩存對象 cache: {}, // 唯一 id種子 uuid:0, // 頁面中每個jQuery副本的唯一標識 expando: "jQuery" + ( jQuery.fn.jquery + Math.random() ).replace( //D/g, "" ), // 是否有關聯的數據 hasData: function(){}, // 設置、讀取自定數據或內部數據 data: function(elem, name, data, pvt) {}, // 移除自定義數據或內部數據 removeData: function(elem, name, pvt) {}, // 設置、讀取內部數據 _data: function(elem, name, data) {}, // 是否可以設置數據 acceptData: function(elem){}});jQuery.fn.extend({ // 設置、讀取自定義數據，解析HTML5屬性data- data: function(key,value){}, // 移除自定義數據 removeData: function(key){}});// 解析HTML5屬性 data-function dataAttr(elem,key,data){}// 檢查數據緩存對象是否為空function isEmptyDataObject(obj){}jQuery.extend({ // 清空數據緩存對象cleanData: function(elems){}});三、$.data(elem, name, data), $.data(elem, name)
$.data(elem, name, data)的使用方法：
如果傳入參數name, data, 則設置任意類型的數據
<!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="http://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：
如果傳入key, 未傳入參數data, 則讀取并返回指定名稱的數據
<!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="http://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) 源碼解析：
jQuery.extend({ // 1. 定義jQuery.data(elem, name, data, pvt) data: function( elem, name, data, pvt /* Internal Use Only */ ) { // 2. 檢查是否可以設置數據 if ( !jQuery.acceptData( elem ) ) { return; // 如果參數elem不支持設置數據，則立即返回 } // 3 定義局部變量 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，為了避免javascript和DOM元素之間循環引用導致的瀏覽器(IE6/7)垃圾回收機制不起作用，要把數據存儲在全局緩存對象jQuery.cache中；對于javascript對象，來及回收機制能夠自動發生，不會有內存泄露的問題，因此數據可以查收存儲在javascript對象上 // 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. 如果是讀取數據，但沒有數據，則返回 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, 說明是在讀取數據 // !id || !cache[id] || (!isEvents && !pvt && !cache[id].data 如果關聯id不存在，說明沒有數據；如果cache[id]不存在，也說明沒有數據；如果是讀取自動以數據，但cache[id].data不存在，說明沒有自定義數據 } // 5. 如果關聯id不存在，則分配一個 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; // 對于DOM元素，jQuery.uuid會自動加1，并附加到DOM元素上 } else { id = internalKey; // 對于javascript對象，關聯id就是jQuery.expando } } // 6. 如果數據緩存對象不存在，則初始化為空對象{} 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; // 對于javascript對象，設置方法toJSON為空函數，以避免在執行JSON.stringify()時暴露緩存數據。如果一個對象定義了方法toJSON(),JSON.stringify()在序列化該對象時會調用這個方法來生成該對象的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. 如果參數name是對象或函數，則批量設置數據 if ( typeof name === "object" || typeof name === "function" ) { if ( pvt ) { cache[ id ] = jQuery.extend( cache[ id ], name ); // 對于內部數據，把參數name中的屬性合并到cache[id]中 } else { cache[ id ].data = jQuery.extend( cache[ id ].data, name ); // 對于自定義數據，把參數name中的屬性合并到cache[id].data中 } } // 8. 如果參數data不是undefined, 則設置單個數據 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. 特殊處理events if ( isEvents && !thisCache[ name ] ) { // 如果參數name是字符串"events",并且未設置過自定義數據"events",則返回事件婚車對象，在其中存儲了事件監聽函數。 return privateCache.events; } // Check for both converted-to-camel and non-converted data property names // If a data property was specified //10. 如果參數name是字符串，則讀取單個數據 if ( getByName ) { // First Try to find as-is property data ret = thisCache[ name ]; // 先嘗試讀取參數name對應的數據 // Test for null|undefined property data if ( ret == null ) { // 如果未取到，則把參數name轉換為駝峰式再次嘗試讀取對應的數據 // Try to find the camelCased property ret = thisCache[ jQuery.camelCase( name ) ]; } } else { // 11. 如果未傳入參數name,data,則返回數據緩存對象 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 ); // 傳入key, value $( "body" ).data( "bar", { myType: "test", count: 40 } ); // 傳入key, value $( "body" ).data( { baz: [ 1, 2, 3 ] } ); // 傳入key, value $( "body" ).data( "foo" ); // 52 // 傳入key $( "body" ).data(); // 未傳入參數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) 源碼解析
jQuery.fn.extend({ // 1. 定義.data(key, value) data: function( key, value ) { var parts, attr, name, data = null; // 2. 未傳入參數的情況 if ( typeof key === "undefined" ) { if ( this.length ) { // 如果參數key是undefined, 即參數格式是.data(), 則調用方法jQuery.data(elem, name, data, pvt)獲取第一個匹配元素關聯的自定義數據緩存對象，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. 參數key 是對象的情況,即參數格式是.data(key),則遍歷匹配元素集合，為每個匹配元素調用方法jQuery.data(elem, name, data,pvt)批量設置數據 } else if ( typeof key === "object" ) { return this.each(function() { jQuery.data( this, key ); }); } // 4. 只傳入參數key的情況 如果只傳入參數key, 即參數格式是.data(key),則返回第一個匹配元素的指定名稱數據 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. 傳入參數key和value的情況 即參數格式是.data(key, value),則為每個匹配元素設置任意類型的數據，并觸發自定義事件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. 函數dataAttr(elem, key, data)解析HTML5屬性data-function dataAttr( elem, key, data ) { // If nothing was found internally, try to fetch any // data from the HTML5 data-* attribute // 只有參數data為undefined時，才會解析HTML5屬性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="http://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="http://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) 源碼解析：
$.extend({ // jQuery.removeData(elem,name,pvt)用于移除通過jQuery.data()設置的數據 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; } // 如果傳入參數name, 則移除一個或多個數據 if ( name ) { thisCache = pvt ? cache[ id ] : cache[ id ].data; if ( thisCache ) { // 只有數據緩存對象thisCache存在時，才有必要移除數據 // 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( " " ); } } } // 遍歷參數name中的數據名，用運算符delete逐個從數據緩存對象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 // 刪除自定義數據緩存對象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 // 刪除數據緩存對象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 // 刪除DOM元素上擴展的jQuery.expando屬性 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="http://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>$.hasData(elem) 源碼解析：$.extend({ hasData: function( elem ) { elem = elem.nodeType ? jQuery.cache[ elem[jQuery.expando] ] : elem[ jQuery.expando ]; return !!elem && !isEmptyDataObject( elem ); // 如果關聯的數據緩存對象存在，并且含有數據，則返回true, 否則返回false。 這里用兩個邏輯非運算符! 把變量elem轉換為布爾值 }});新聞熱點
疑難解答
