jQuery Metadata

     jQuery metadata可以说是jQuery插件的插件，用jQuery写插件的朋友都知道，大多数情况下我们要收入jQuery.metadata，它是出自jQuery官方的，2.0版本以后的都用起来很方便，具体作用是从dom对象提取元数据并返回此对象，要想会用的话，那可以好好看看官方文档了。

下面是官方的文档：

metadata( options )	Returns: Object
Extracts, caches, and returns metadata from the first element in the jQuery collection.
jQuery.metadata.setType( type, name )	Returns: null
Sets the default type and name options for all following metadata requests.
jQuery.metadata.get( elem, options )	Returns: Object
Extracts metadata from an element.

1、metadata(options)
Extracts, caches, and returns metadata from the first element in the jQuery collection.

Arguments:

options (Optional)	Options
A set of key/value pairs that define the type of metadata to be extracted. All options are optional.

Options:

type	String	Default: 'class'
Specify the expected locations of metadata for the element. Possible values are 'class': search in the class attribute, 'elem': search for an element inside the element being searched, and 'attr': search in a custom attribute on the element.
Code Searches for metadata in a custom element attribute instead of in the class. $(".selector").metadata({ type: 'attr' })
name	String	Default: 'metadata'
When type is 'attr', specify the name of the custom attribute for which to search. When type is 'elem', specify the tag name of the element for which to search.
Code Searches for metadata in a custom element attribute with a name of 'jdata'. $(".selector").metadata({ type: 'attr', name: 'jdata' })
single	String	Default: 'metadata'
The name given to the data extracted from the element in the jQuery cache.
Code Stores and retrieves the data extracted into an item named 'jdata' in the jQuery cache. $(".selector").metadata({ single: 'jdata' })

Examples:

• Code

Gets metadata from the class attribute.

<li class="someclass {some: 'data'} anotherclass">...</li>

<script>alert($('li.someclass').metadata().some);</script>

• Code

Gets metadata from a custom attribute.

<li data="{some:'random', json: 'data'}">...</li>

<script>alert($('li.someclass').metadata({type:'attr',name:'data'}).some);</script>

• Code

Gets metadata from a child element.

<li class="someclass"><script type="application/json">{some:"json",data:true}</script>...</li>

<script>alert($('li.someclass').metadata({type:'elem',name:'script'}).some);</script>

2、jQuery.metadata.setType(type,name)

Sets the default type and name options for all following metadata requests.

Arguments:

type	String
Specify the expected location of metadata for the element. Possible values are 'class' (default): search in the class attribute, 'elem': search for an element inside the element being searched, and 'attr': search in a custom attribute on the element.
name	String
The name of the tag or attribute for which to search depending on the value of the 'type' option.

Examples:

• Code

Setup metadata plugin to look for a custom attribute.

<li data="{some:'random', json: 'data'}" class="someclass">...</li>

<script>
$.metadata.setType('attr','data');
alert($('li.someclass').metadata().some);
</script>

3、jQuery.metadata.get( elem, [options] )

Extracts metadata from an element.

Arguments:

elem	Element
The element containing the metadata to be extracted.
options (Optional)	Options
A set of key/value pairs that define the type of metadata to be extracted. All options are optional. See the metadata plugin page for more information.

Examples:

• Code

Setup metadata plugin to look for a custom attribute.

<li class="someclass {some:'random', json: 'data'}">...</li>

<script>
$('li.someclass').each(function(){
    var data = $.metadata.get(this);
    alert(data.some);
});
</script>