diff --git a/polygerrit-ui/app/elements/diff/gr-diff/gr-diff-utils.js b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff-utils.js
new file mode 100644
index 0000000..7eee071
--- /dev/null
+++ b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff-utils.js
@@ -0,0 +1,40 @@
+/**
+ * @license
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/** @enum {string} */
+export const DiffSide = {
+  LEFT: 'left',
+  RIGHT: 'right',
+};
+
+/**
+ * Compare two ranges. Either argument may be falsy, but will only return
+ * true if both are falsy or if neither are falsy and have the same position
+ * values.
+ *
+ * @param {Range=} a range 1
+ * @param {Range=} b range 2
+ * @return {boolean}
+ */
+export function rangesEqual(a, b) {
+  if (!a && !b) { return true; }
+  if (!a || !b) { return false; }
+  return a.start_line === b.start_line &&
+      a.start_character === b.start_character &&
+      a.end_line === b.end_line &&
+      a.end_character === b.end_character;
+}