Improve code quality and write tests

node_modules/regenerator-transform/src/util.js

@@ -0,0 +1,45 @@
+/**
+ * Copyright (c) 2014-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+let currentTypes = null;
+
+export function wrapWithTypes(types, fn) {
+  return function (...args) {
+    const oldTypes = currentTypes;
+    currentTypes = types;
+    try {
+      return fn.apply(this, args);
+    } finally {
+      currentTypes = oldTypes;
+    }
+  };
+}
+
+export function getTypes() {
+  return currentTypes;
+}
+
+export function runtimeProperty(name) {
+  const t = getTypes();
+  return t.memberExpression(
+    t.identifier("regeneratorRuntime"),
+    t.identifier(name),
+    false
+  );
+}
+
+export function isReference(path) {
+  return path.isReferenced() || path.parentPath.isAssignmentExpression({ left: path.node });
+}
+
+export function replaceWithOrRemove(path, replacement) {
+  if (replacement) {
+    path.replaceWith(replacement)
+  } else {
+    path.remove();
+  }
+}