Avoid unnecessary re-render on CHECK_NETWORK_STATUS

ts/util/assignWithNoUnnecessaryAllocation.ts

@@ -0,0 +1,32 @@
+// Copyright 2020 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import { has } from 'lodash';
+
+/**
+ * This function is like `Object.assign` but won't create a new object if we don't need
+ * to. This is purely a performance optimization.
+ *
+ * This is useful in places where we don't want to create a new object unnecessarily,
+ * like in reducers where we might cause an unnecessary re-render.
+ *
+ * See the tests for the specifics of how this works.
+ */
+// We want this to work with any object, so we allow `object` here.
+// eslint-disable-next-line @typescript-eslint/ban-types
+export function assignWithNoUnnecessaryAllocation<T extends object>(
+  obj: Readonly<T>,
+  source: Readonly<Partial<T>>
+): T {
+  // We want to bail early so we use `for .. in` instead of `Object.keys` or similar.
+  // eslint-disable-next-line no-restricted-syntax
+  for (const key in source) {
+    if (!has(source, key)) {
+      continue;
+    }
+    if (!(key in obj) || obj[key] !== source[key]) {
+      return { ...obj, ...source };
+    }
+  }
+  return obj;
+}