在jQuery早期版本中(1.12):使用data()方法为DOM元素附加数据时,会为DOM元素附加一个名为'jquery'+一堆数字的属性,这个属性的值为数字。通过这个属性找到对应缓存池中的缓存对象进而进行操作,避免了直接附加引用类型的数据到DOM元素上。听老师说这样可以防止内存泄漏。
而在jQuery3.1版本的源码中,也会给DOM元素附加一个名为'jQuery'+一堆数字的属性,但是 这个属性的值为对象。 我想问一下,在jQuery3.1的版本中是如何防止内存泄漏的?
下面是1.12版本data的源码:
define([ "../core", "../var/rnotwhite", "./accepts" ], function( jQuery, rnotwhite ) { function Data() { // Support: Android<4, // Old WebKit does not have Object.preventExtensions/freeze method, // return new empty object instead with no [[set]] accessor Object.defineProperty( this.cache = {}, 0, { get: function() { return {}; } }); this.expando = jQuery.expando + Math.random(); } Data.uid = 1; Data.accepts = jQuery.acceptData; Data.prototype = { key: function( owner ) { // We can accept data for non-element nodes in modern browsers, // but we should not, see #8335. // Always return the key for a frozen object. if ( !Data.accepts( owner ) ) { return 0; } var descriptor = {}, // Check if the owner object already has a cache key unlock = owner[ this.expando ]; // If not, create one if ( !unlock ) { unlock = Data.uid++; // Secure it in a non-enumerable, non-writable property try { descriptor[ this.expando ] = { value: unlock }; Object.defineProperties( owner, descriptor ); // Support: Android<4 // Fallback to a less secure definition } catch ( e ) { descriptor[ this.expando ] = unlock; jQuery.extend( owner, descriptor ); } } // Ensure the cache object if ( !this.cache[ unlock ] ) { this.cache[ unlock ] = {}; } return unlock; }, set: function( owner, data, value ) { var prop, // There may be an unlock assigned to this node, // if there is no entry for this "owner", create one inline // and set the unlock as though an owner entry had always existed unlock = this.key( owner ), cache = this.cache[ unlock ]; // Handle: [ owner, key, value ] args if ( typeof data === "string" ) { cache[ data ] = value; // Handle: [ owner, { properties } ] args } else { // Fresh assignments by object are shallow copied if ( jQuery.isEmptyObject( cache ) ) { jQuery.extend( this.cache[ unlock ], data ); // Otherwise, copy the properties one-by-one to the cache object } else { for ( prop in data ) { cache[ prop ] = data[ prop ]; } } } return cache; }, get: function( owner, key ) { // Either a valid cache is found, or will be created. // New caches will be created and the unlock returned, // allowing direct access to the newly created // empty data object. A valid owner object must be provided. var cache = this.cache[ this.key( owner ) ]; return key === undefined ? cache : cache[ key ]; }, access: function( owner, key, value ) { var stored; // 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) ) { stored = this.get( owner, key ); return stored !== undefined ? stored : this.get( owner, jQuery.camelCase(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; }, remove: function( owner, key ) { var i, name, camel, unlock = this.key( owner ), cache = this.cache[ unlock ]; if ( key === undefined ) { this.cache[ unlock ] = {}; } else { // Support array or space separated string of keys if ( jQuery.isArray( key ) ) { // If "name" is an array of keys... // When data is initially created, via ("key", "val") signature, // keys will be converted to camelCase. // Since there is no way to tell _how_ a key was added, remove // both plain key and camelCase key. #12786 // This will only penalize the array argument path. name = key.concat( key.map( jQuery.camelCase ) ); } else { camel = jQuery.camelCase( key ); // Try the string as a key before any manipulation if ( key in cache ) { name = [ key, camel ]; } else { // If a key with the spaces exists, use it. // Otherwise, create an array by matching non-whitespace name = camel; name = name in cache ? [ name ] : ( name.match( rnotwhite ) || [] ); } } i = name.length; while ( i-- ) { delete cache[ name[ i ] ]; } } }, hasData: function( owner ) { return !jQuery.isEmptyObject( this.cache[ owner[ this.expando ] ] || {} ); }, discard: function( owner ) { if ( owner[ this.expando ] ) { delete this.cache[ owner[ this.expando ] ]; } } }; return Data; });
下面是3.1版本中data的源码
function Data() { this.expando = jQuery.expando + Data.uid++; } Data.uid = 1; Data.prototype = { cache: function( owner ) { // Check if the owner object already has a cache 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. if ( acceptData( owner ) ) { // If it is a node unlikely to be stringify-ed or looped over // use plain assignment 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 } else { Object.defineProperty( owner, this.expando, { value: value, configurable: true } ); } } } return value; }, 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: function( owner, key ) { return key === undefined ? this.cache( owner ) : // Always use camelCase key (gh-2257) owner[ this.expando ] && owner[ this.expando ][ jQuery.camelCase( key ) ]; }, 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; }, 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 ( jQuery.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 ]; } } }, hasData: function( owner ) { var cache = owner[ this.expando ]; return cache !== undefined && !jQuery.isEmptyObject( cache ); } };
我也觉得好神奇,居然可以是对象。
等我弄明白了我会告诉你的!