jQuery.data方法

先看用法：

看jq源码

<span style="font-size:14px;">var data_userfunction Data() {Object.defineProperty( this.cache = {}, 0, { get: function() { return {};}});this.expando = jQuery.expando + Math.random();}Data.uid = 1;Data.accepts = function( owner ) {return owner.nodeType ? owner.nodeType === 1 || owner.nodeType === 9 : true;};Data.prototype = {key: function( owner ) {if ( !Data.accepts( owner ) ) {return 0;}var descriptor = {},unlock = owner[ this.expando ];if ( !unlock ) {unlock = Data.uid++;try { descriptor[ this.expando ] = { value: unlock };Object.defineProperties( owner, descriptor );  } catch ( e ) {descriptor[ this.expando ] = unlock; jQuery.extend( owner, descriptor );}}if ( !this.cache[ unlock ] ) { this.cache[ unlock ] = {};} return unlock;},set: function( owner, data, value ) {var prop,unlock = this.key( owner ),cache = this.cache[ unlock ];if ( typeof data === "string" ) {cache[ data ] = value;} else {if ( jQuery.isEmptyObject( cache ) ) {jQuery.extend( this.cache[ unlock ], data );} else { for ( prop in data ) { cache[ prop ] = data[ prop ]; } } } return cache;},get: function( owner, key ) {var cache = this.cache[ this.key( owner ) ]; return key === undefined ? cache : cache[ key ]; },access: function( owner, key, value ) {var stored;if ( key === undefined || ((key && typeof key === "string") && value === undefined) ) { stored = this.get( owner, key ); return stored !== undefined ? stored : this.get( owner, jQuery.camelCase(key) );}this.set( owner, key, value );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 {if ( jQuery.isArray( key ) ) {name = key.concat( key.map( jQuery.camelCase ) );} else {camel = jQuery.camelCase( key );if ( key in cache ) {name = [ key, camel ];} else {// If a key with the spaces exists, use it.// Otherwise, create an array by matching non-whitespacename = camel;name = name in cache ?[ name ] : ( name.match( core_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 ] ];}}};data_user = new Data();jQuery.extend({acceptData: Data.accepts,hasData: function( elem ) {return data_user.hasData( elem );},data: function( elem, name, data ) {return data_user.access( elem, name, data );},removeData: function( elem, name ) {data_user.remove( elem, name );}});</span>

1、

Data构造函数，defineProperty的作用：定义Data.cache = { 0：function(){return {}} }，这里的k值和方法是不能修改，this.expando，取一个随机数

function Data() {
    Object.defineProperty( this.cache = {}, 0, {
        get: function() {
            return {};
        }
    });

    this.expando = jQuery.expando + Math.random();
}

2、

$.data()方法，实际调用的是Data的实例方法

data_user = new Data();
jQuery.extend({
    acceptData: Data.accepts,

    hasData: function( elem ) {
        return data_user.hasData( elem ) || data_priv.hasData( elem );
    },

    data: function( elem, name, data ) {
        return data_user.access( elem, name, data );
    },

    removeData: function( elem, name ) {
        data_user.remove( elem, name );
    }
});

3

这里做的判断意思是：当传入的对象有nodeType，并且等于1（元素）或9（document），或者是其他对象，就返回真

Data.accepts = function( owner ) {
    return owner.nodeType ?
        owner.nodeType === 1 || owner.nodeType === 9 : true;
};

4、this.expando是随机数，放到对象身上。unlock是cache的k值

对应关系：{this.expando: unlock}，cache = {unlock: value}

key: function( owner ) {

    //这里进行筛选，只有通过的对象才能继续，没有通过的对象都返回0，因为0不能修改，不能通过的对象所有取值都是{}。

    if ( !Data.accepts( owner ) ) {
        return 0;
    }
    //descriptor后面会赋值为：{this.expando: unlock}

    var descriptor = {},
        unlock = owner[ this.expando ];

    //如果unlock不存在，就赋值Data.uid++，并且给传入对象(假如为obj)赋值：obj[this.expando] = unlock

    if ( !unlock ) {
        unlock = Data.uid++;
        try {
            descriptor[ this.expando ] = { value: unlock };
            Object.defineProperties( owner, descriptor );
        } catch ( e ) {
            descriptor[ this.expando ] = unlock;
            jQuery.extend( owner, descriptor );
        }
    }

    //缓存，和obj的unlock对应起来

    if ( !this.cache[ unlock ] ) {
        this.cache[ unlock ] = {};
    }

    return unlock;
}

5、set为赋值操作

set: function( owner, data, value ) {
    var prop,

        //获取对象对应缓存的k值，并且通过k值取出缓存空间

        unlock = this.key( owner ),
        cache = this.cache[ unlock ];
    //这里为for in循环赋值
    if ( typeof data === "string" ) {
        cache[ data ] = value;
    } else {
        if ( jQuery.isEmptyObject( cache ) ) {
            jQuery.extend( this.cache[ unlock ], data );
        } else {
            for ( prop in data ) {
                cache[ prop ] = data[ prop ];
            }
        }
    }
    return cache;
}

6、通过传入对象，要取的K值，获取对应的值。如果传入的key没有，则返回所有缓存的值

get: function( owner, key ) {
    var cache = this.cache[ this.key( owner ) ];

    return key === undefined ?
        cache : cache[ key ];
}

7、

access方法，通过传入的参数值，分别调用赋值/取值方法

8、

remove方法：删除缓存中对应的K值

hasData方法：判断对象身上是否有缓存（对应的cache中是否还存在有值）

discard：删除对象身上的随机数值，作用彻底清空和缓存的绑定关系