reorganize directory and file structure

lib/util/util.js

@@ -0,0 +1,27 @@
+// zip two arrays
+export function zip(a, b) {
+  return a.map((k, i) => [k, b[i]]);
+}
+
+export function capitalizeFirstLetter(val) {
+  return String(val).charAt(0).toUpperCase() + String(val).slice(1);
+}
+
+const _mapRecursiveStructure = mapping => transform => root => {
+  const found = mapping.get(root);
+  if (found) {
+    // already mapped
+    // return existing result to prevent endless recursion
+    return found;
+  }
+  // note the indirection (wrapped in lamda), this allows the user to recursively map the children (which may refer to the root) without yet having finished mapping the root.
+  let memo;
+  const result = () => {
+    // memoization is necessary for correctness
+    return memo || (memo = transform(root, _mapRecursiveStructure(mapping)(transform)));
+  };
+  mapping.set(root, result);
+  return result;
+};
+
+export const mapRecursiveStructure = _mapRecursiveStructure(new Map());