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    <p>You either extend objects (which is bad for host objects) or you wrap the objects as jQuery does, using the wrapped object to identify associated data in the hash table. In essence you hash the DOM node and do a lookup in a hash table for the associated data. Of course you still need to extend the host object, but you add only a single property which you know to be reasonably safe to add across browsers, rather than a set of arbitrary properties. If you inspect an element with associated data you might see something like element.jQuery171023696433915756643, which contains the internal storage index for that element. I would recommend reading the jQuery source if you are that interested, particularly the data() function</p> <pre><code>data: function( elem, name, data, pvt /* Internal Use Only */ ) { if ( !jQuery.acceptData( elem ) ) { return; } var privateCache, thisCache, ret, internalKey = jQuery.expando, getByName = typeof name === "string", // We have to handle DOM nodes and JS objects differently because IE6-7 // can't GC object references properly across the DOM-JS boundary isNode = elem.nodeType, // Only DOM nodes need the global jQuery cache; JS object data is // attached directly to the object so GC can occur automatically cache = isNode ? jQuery.cache : elem, // Only defining an ID for JS objects if its cache already exists allows // the code to shortcut on the same path as a DOM node with no cache id = isNode ? elem[ internalKey ] : elem[ internalKey ] &amp;&amp; internalKey, isEvents = name === "events"; // Avoid doing any more work than we need to when trying to get data on an // object that has no data at all if ( (!id || !cache[id] || (!isEvents &amp;&amp; !pvt &amp;&amp; !cache[id].data)) &amp;&amp; getByName &amp;&amp; data === undefined ) { return; } if ( !id ) { // Only DOM nodes need a new unique ID for each element since their data // ends up in the global cache if ( isNode ) { elem[ internalKey ] = id = ++jQuery.uuid; } else { id = internalKey; } } if ( !cache[ id ] ) { cache[ id ] = {}; // Avoids exposing jQuery metadata on plain JS objects when the object // is serialized using JSON.stringify if ( !isNode ) { cache[ id ].toJSON = jQuery.noop; } } // An object can be passed to jQuery.data instead of a key/value pair; this gets // shallow copied over onto the existing cache if ( typeof name === "object" || typeof name === "function" ) { if ( pvt ) { cache[ id ] = jQuery.extend( cache[ id ], name ); } else { cache[ id ].data = jQuery.extend( cache[ id ].data, name ); } } privateCache = thisCache = cache[ id ]; // jQuery data() is stored in a separate object inside the object's internal data // cache in order to avoid key collisions between internal data and user-defined // data. if ( !pvt ) { if ( !thisCache.data ) { thisCache.data = {}; } thisCache = thisCache.data; } if ( data !== undefined ) { thisCache[ jQuery.camelCase( name ) ] = data; } // Users should not attempt to inspect the internal events object using jQuery.data, // it is undocumented and subject to change. But does anyone listen? No. if ( isEvents &amp;&amp; !thisCache[ name ] ) { return privateCache.events; } // Check for both converted-to-camel and non-converted data property names // If a data property was specified if ( getByName ) { // First Try to find as-is property data ret = thisCache[ name ]; // Test for null|undefined property data if ( ret == null ) { // Try to find the camelCased property ret = thisCache[ jQuery.camelCase( name ) ]; } } else { ret = thisCache; } return ret; } </code></pre>
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    1. POhow to code around storing data (objects, custom attributes) on DOM nodes
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    1. USMatt Esch
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    1. POhow to code around storing data (objects, custom attributes) on DOM nodes
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    1. COI guess this question kind of "evolved" into a, [how jQuery data function works](http://stackoverflow.com/questions/5948099/jquery-data-how-to-work-question). So it would seem that there really isn't a way around this, and at the very minimum a single attribute (e.g. hash name) has to be set to the DOM node. Also, from the comments in the jQuery code it appears that only IE6-7 are problematic for GC?
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    2. COI think I get it now, each DOM object with tied data is extended with the same arbitrary random property name that contains a numeric index into a global array that points to the key/value of the data. So there isn't really a way around not extending the host object at least a little bit.
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    3. COYes. When isn't IE6/7 problematic for GC :P. If you want to learn more about this I suggest reading http://javascript.info/tutorial/memory-leaks - "jQuery anti-leak measures and leaks"
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