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jQuery中的Data()源码问题

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悬赏园豆:20 [待解决问题]

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;
});
View Code

 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 );
    }
};
View Code
MnCu的主页 MnCu | 初学一级 | 园豆:158
提问于:2016-11-26 20:44
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所有回答(1)
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我也觉得好神奇,居然可以是对象。

angelshelter | 园豆:9687 (大侠五级) | 2016-12-19 22:19

等我弄明白了我会告诉你的! 

支持(0) 反对(0) MnCu | 园豆:158 (初学一级) | 2016-12-19 22:22
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