--- /dev/null
+var Set = require('./es6.set')
+ , from = require('./_array-from-iterable')
+ , metadata = require('./_metadata')
+ , anObject = require('./_an-object')
+ , getPrototypeOf = require('./_object-gpo')
+ , ordinaryOwnMetadataKeys = metadata.keys
+ , toMetaKey = metadata.key;
+
+var ordinaryMetadataKeys = function(O, P){
+ var oKeys = ordinaryOwnMetadataKeys(O, P)
+ , parent = getPrototypeOf(O);
+ if(parent === null)return oKeys;
+ var pKeys = ordinaryMetadataKeys(parent, P);
+ return pKeys.length ? oKeys.length ? from(new Set(oKeys.concat(pKeys))) : pKeys : oKeys;
+};
+
+metadata.exp({getMetadataKeys: function getMetadataKeys(target /*, targetKey */){
+ return ordinaryMetadataKeys(anObject(target), arguments.length < 2 ? undefined : toMetaKey(arguments[1]));
+}});
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