This article introduces to you the methods of data operation in jQuery and the definition of jQuery. It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.
There are two methods for data operations in jQuery
$().data() $.data(elem);
The internal implementation is inseparable from custom classesData
Data
##Data is defined in src/data/Data.js, and the expando attribute is added to the instance when building, as a unique Identification
function Data() {
this.expando = jQuery.expando + Data.uid++;
}Data.prototype = {
cache: function(){
...
},
set: function(){
...
},
get: function(){
...
},
access: function(){
...
},
remove: function(){
...
},
hasData: function(){
...
}
}Object.defineProperty to define data for it. The property name is also expando and initialized to {}. At the same time, the property descriptor can be changed and cannot be enumerated.
cache: function( owner ) {
// Check if the owner object already has a cache
// 获取在owner的缓存值
var value = owner[ this.expando ];
// If not, create one
if ( !value ) {
value = {};
// We can accept data for non-element nodes in modern browsers,
// but we should not, see #8335.
// Always return an empty object.
// 判断owener类型 是否能在其上调用data
// 在元素节点或body或对象上可以设置data
// 其他节点不设置缓存数据
if ( acceptData( owner ) ) {
// If it is a node unlikely to be stringify-ed or looped over
// use plain assignment
// 此处为owner添加属性 key为Data对象的expando值 建立owner和Data对象之间的连接
// owner是元素节点或body
if ( owner.nodeType ) {
owner[ this.expando ] = value;
// Otherwise secure it in a non-enumerable property
// configurable must be true to allow the property to be
// deleted when data is removed
// owner是对象
// 为owner添加expando属性 初始化为{},同时属性描述符可以更改，不可枚举
} else {
Object.defineProperty( owner, this.expando, {
value: value,
configurable: true
} );
}
}
}
return value;
}set to update the cache object, which is divided into data(key,value) or data(obj) In both calling cases, the key name must be saved in camel case when saving.
set: function( owner, data, value ) {
var prop,
cache = this.cache( owner );
// Handle: [ owner, key, value ] args
// Always use camelCase key (gh-2257)
if ( typeof data === "string" ) {
cache[ jQuery.camelCase( data ) ] = value;
// Handle: [ owner, { properties } ] args
} else {
// Copy the properties one-by-one to the cache object
for ( prop in data ) {
cache[ jQuery.camelCase( prop ) ] = data[ prop ];
}
}
return cache;
}get to obtain the cache object. When calling, there is data(key) and data(). If the key is not specified, the entire cache object is returned directly, otherwise cache[key] is returned. Key names must also be converted to camel case.
get: function( owner, key ) {
return key === undefined ?
this.cache( owner ) :
// Always use camelCase key (gh-2257)
owner[ this.expando ] && owner[ this.expando ][ jQuery.camelCase( key ) ];
}set or get
string and value===undefined corresponds to obtaining the specified value
set, in setInternal differentiation
<div class="code" style="position:relative; padding:0px; margin:0px;"><pre class="brush:php;toolbar:false"> access: function( owner, key, value ) {
// In cases where either:
//
// 1. No key was specified
// 2. A string key was specified, but no value provided
//
// Take the "read" path and allow the get method to determine
// which value to return, respectively either:
//
// 1. The entire cache object
// 2. The data stored at the key
//
if ( key === undefined ||
( ( key && typeof key === "string" ) && value === undefined ) ) {
return this.get( owner, key );
}
// When the key is not a string, or both a key and value
// are specified, set or extend (existing objects) with either:
//
// 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;
}</pre><div class="contentsignin">Copy after login</div></div>Use to delete cached object attributes , when calling, you can pass in a string representing the key name to be deleted, or pass in a string array that holds multiple key names. Key names must also be converted to camel case. If no parameters are passed in or out, the cached data object on the owner will be deleted directly.
<div class="code" style="position:relative; padding:0px; margin:0px;"><pre class="brush:php;toolbar:false"> remove: function( owner, key ) {
var i,
cache = owner[ this.expando ];
if ( cache === undefined ) {
return;
}
if ( key !== undefined ) {
// Support array or space separated string of keys
if ( Array.isArray( key ) ) {
// If key is an array of keys...
// We always set camelCase keys, so remove that.
key = key.map( jQuery.camelCase );
} else {
key = jQuery.camelCase( key );
// If a key with the spaces exists, use it.
// Otherwise, create an array by matching non-whitespace
key = key in cache ?
[ key ] :
( key.match( rnothtmlwhite ) || [] );
}
i = key.length;
while ( i-- ) {
delete cache[ key[ i ] ];
}
}
// Remove the expando if there's no more data
if ( key === undefined || jQuery.isEmptyObject( cache ) ) {
// Support: Chrome <=35 - 45
// Webkit & Blink performance suffers when deleting properties
// from DOM nodes, so set to undefined instead
// https://bugs.chromium.org/p/chromium/issues/detail?id=378607 (bug restricted)
if ( owner.nodeType ) {
owner[ this.expando ] = undefined;
} else {
delete owner[ this.expando ];
}
}
}</pre><div class="contentsignin">Copy after login</div></div>Determine whether there is cached data on the owner. <div class="code" style="position:relative; padding:0px; margin:0px;"><pre class="brush:php;toolbar:false"> hasData: function( owner ) {
var cache = owner[ this.expando ];
return cache !== undefined && !jQuery.isEmptyObject( cache );
}</pre><div class="contentsignin">Copy after login</div></div>Inner class after definition
dataAfter that, expand in /src/data.js. Added hasData, data, removeData, _data, _removeData and other methods to jQuery, in jQuery.fn Added data and removeData methods. The methods expanded in jQuery are all encapsulations of the Data method. When calling
, there is no pairing of set and The get operation is distinguished, and set and get are distinguished internally in Data.prototype.access. In the source code below, dataUser and dataPriv are Data instances, which respectively cache data and indicate whether the jq object adds the element's data attribute to dataUser中<div class="code" style="position:relative; padding:0px; margin:0px;"><pre class="brush:php;toolbar:false">// $.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 );
}
} );</pre><div class="contentsignin">Copy after login</div></div>The only methods extended on
are data and removeData. In data, first handle the two calling situations $().data() and $().data({k:v}) . If it is the first case, the cached data object on this[0] is returned. If it is the first time to call $().data(), at the same time The data attribute on the element will also be added to dataUser, and dataPriv will be updated. If it is the calling method of $().data({k:v}), the jq object is traversed and the cached data is updated for each node. Other calling methods such as $().data(k) and $().data(k,v) call access for processing. The access here is not Data.prototype.access.
Traverse the jq object and delete the cached data on each node. <div class="code" style="position:relative; padding:0px; margin:0px;"><pre class="brush:php;toolbar:false">// $().data
jQuery.fn.extend( {
data: function( key, value ) {
var i, name, data,
elem = this[ 0 ], // elem为dom对象
attrs = elem && elem.attributes; // 节点上的属性
// Gets all values
// $().data()
if ( key === undefined ) {
if ( this.length ) {
data = dataUser.get( elem );
// elem是元素节点，且dataPriv中无hasDataAttrs时执行这个代码块里的代码
// dataPriv上的hasDataAttrs表示elem是否有data-xxx属性
// 初始化dataPriv后花括号内的代码不再执行，即以下的if内的代码只执行一次
if ( elem.nodeType === 1 && !dataPriv.get( elem, "hasDataAttrs" ) ) {
i = attrs.length;
while ( i-- ) {
// Support: IE 11 only
// The attrs elements can be null (#14894)
// 将elem的data-*-*属性以*-*转为驼峰命名方式的值为键
// 在dataAttr函数内保存到dataUser中
// 所以用$().data可以获取元素的data-*属性 但修改后dom上的属性却不变化
if ( attrs[ i ] ) {
name = attrs[ i ].name;
// name为data-xxx
if ( name.indexOf( "data-" ) === 0 ) {
// name为xxx
name = jQuery.camelCase( name.slice( 5 ) );
dataAttr( elem, name, data[ name ] );
}
}
}
// 同时将dataPriv的hasDataAttrs属性设置为真，表示已经将元素属性节点上的data属性保存到缓存对象中
dataPriv.set( elem, "hasDataAttrs", true );
}
}
return data;
}
// Sets multiple values
// $().data(obj) 此处遍历this，即遍历jq对象上所有的节点，并在其设置值
if ( typeof key === "object" ) {
return this.each( function() {
dataUser.set( this, key );
} );
}
// 除了$().data()和$().data({k:v})的其他情况
return access( this, function( value ) {
var data;
// The calling jQuery object (element matches) is not empty
// (and therefore has an element appears at this[ 0 ]) and the
// `value` parameter was not undefined. An empty jQuery object
// will result in `undefined` for elem = this[ 0 ] which will
// throw an exception if an attempt to read a data cache is made.
// value undefined说明是获取操作
// 调用$().data(k)
if ( elem && value === undefined ) {
// Attempt to get data from the cache
// The key will always be camelCased in Data
// 从dataUser中获取 非undefined时返回
data = dataUser.get( elem, key );
if ( data !== undefined ) {
return data;
}
// Attempt to "discover" the data in
// HTML5 custom data-* attrs
// dataUser中不存在key，调用dataAttr查找元素的data-*属性
// 如果存在属性，更新dataUser并返回其值
data = dataAttr( elem, key );
if ( data !== undefined ) {
return data;
}
// We tried really hard, but the data doesn&#39;t exist.
return;
}
// Set the data...
// jq对象长度 >= 1, 调用如$().data(k,v) 遍历jq对象，为每个节点设置缓存数据
this.each( function() {
// We always store the camelCased key
dataUser.set( this, key, value );
} );
}, null, value, arguments.length > 1, null, true );
},
// 遍历jq对象，删除各个元素上的缓存数据
removeData: function( key ) {
return this.each( function() {
dataUser.remove( this, key );
} );
}
} );</pre><div class="contentsignin">Copy after login</div></div>Among them, getData
is used to perform type conversion on the data attribute on the element, and dataAttr is used to obtain the data attribute saved on the element node and update it at the same time. dataUser. It should be noted that when calling in the $().data(k, v) method, if the attribute cannot be found on the cached data, dataAttr will be called to find the attribute on the element. . <div class="code" style="position:relative; padding:0px; margin:0px;"><pre class="brush:php;toolbar:false">// 属性值是string 进行类型转换
function getData( data ) {
if ( data === "true" ) {
return true;
}
if ( data === "false" ) {
return false;
}
if ( data === "null" ) {
return null;
}
// Only convert to a number if it doesn't change the string
// data转化成number再转成string后仍严格等于data
if ( data === +data + "" ) {
return +data;
}
if ( rbrace.test( data ) ) {
return JSON.parse( data );
}
return data;
}
// 获取元素的dataset中的属性，并保存到dataUser中
function dataAttr( elem, key, data ) {
var name;
// If nothing was found internally, try to fetch any
// data from the HTML5 data-* attribute
// 此处获取dataset里的值
if ( data === undefined && elem.nodeType === 1 ) {
name = "data-" + key.replace( rmultiDash, "-$&" ).toLowerCase(); // 此处将驼峰命名方式的key转化为data-*-*
data = elem.getAttribute( name );
if ( typeof data === "string" ) {
try {
data = getData( data );
} catch ( e ) {}
// Make sure we set the data so it isn't changed later
// 将元素的data-*属性保存到dataUser中
dataUser.set( elem, key, data );
} else {
data = undefined;
}
}
return data;
}</pre><div class="contentsignin">Copy after login</div></div> Recommended related articles:
How to use JavaScript functions? Introduction to the properties and methods of JavaScript functions
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