Refactor - Move traverse to separate file and export from index

src/traverse.ts

@@ -0,0 +1,15 @@
+// import { isNodeSimple } from './utils';
+import {FiberNode} from './mocked-types';
+
+function traverse(node: FiberNode, fn: (node: FiberNode) => any) {
+  fn.call(null, node);
+
+  if (node.child !== null) {
+    traverse(node.child, fn);
+  }
+  if (node.sibling !== null) {
+    traverse(node.sibling, fn);
+  }
+};
+
+export default traverse;