/**
 * Object.keys(object) -> Array of String
 *
 * List the keys that belongs only to the given object.
 **/
(function() {
     function list_keys(object) {
	 var prop
	   , keys = [];

	 for (prop in object) {
             object.hasOwnProperty(prop) && keys.push(prop);
	 }
	 return keys;
     }

     Object.keys || (Object.keys = list_keys)
}());