var $D = (function(){
 var camelize = function(string){
     return string.replace(/-+(.)?/g, function(match, chr) {
       return chr ? chr.toUpperCase() : '';
     });
 };
 return function(element){
  if( element.dataset ) return element.dataset;
  var sets = {};
  for(var i=0,a=element.attributes,l=a.length;i<l;i++){
   var attr = a[i];
   if( !attr.name.match(/^data-/) ) continue;
   sets[camelize(attr.name.replace(/^data-/,''))] = attr.value;
  }
  return sets;
 };
})();

<li id="xyz" data-length="1" data-foo-bar='1' data-something="hello">test</li>

alert(JSON.stringify( $D(document.getElementById('xyz')) )); // { length:1 ,fooBar:1,something:"hello" }