diff --git a/lib/traverse.js b/lib/traverse.js
index 9388e95..c16938a 100644
--- a/lib/traverse.js
+++ b/lib/traverse.js
@@ -82,7 +82,10 @@ function Traverse (refObj) {
             state.notLeaf = !state.isLeaf;
             state.notRoot = !state.isRoot;
             
-            f.call(state, node);
+            // use return values to update if defined
+            var ret = f.call(state, node);
+            if (ret !== undefined) state.update(ret);
+            
             if (typeof state.node == 'object'
             && state.node !== null && !state.circular) {
                 parents.push(state);