easy way to get a list of every expando property on all the supplied element in a list

element_expandos.js

var val = [document, new Date(), true, 1, 'foo'];
'a abbr acronym address area article aside audio b bdi bdo big blockquote body br button canvas caption '
+ 'cite code col colgroup command datalist dd del details dfn div dl dt em embed fieldset figcaption '
+ 'figure footer form frame frameset h1 h2 h3 h4 h5 h6 head header hgroup hr html i iframe img input ins '
+ 'kbd keygen label legend li link map mark meta meter nav noscript object ol optgroup option output p '
+ 'param pre progress q rp rt ruby samp script section select small source span split strong style sub '
+ 'summary sup table tbody td textarea tfoot th thead time title tr track tt ul var video wbr'.split( ' ' ).map( function( tag ) {
	var el = document.createElement( tag );
	return Object.getOwnPropertyNames( el ).filter( function( attr ) {
		var value = val.concat( [attr] ), i = value.length;
		while ( --i >= 0 ) {
			try {
				el[attr] = value[i];
				if ( el[attr] === value[i] )
					return true;
			}
			catch ( e ) {
				console.log( 'FAILED: ', el.tagName, ', property: ', attr, ', value: ', value[i] );
			}
		}
		return false;
	} ).sort().join( ' ' );
} ).join( ' ' ).split( ' ' ).sort().reduce( function( res, attr ) {
	res.indexOf( attr ) > -1 || res.push( attr );
	return res;
}, [] ).join( ' ' );