diff --git a/static/js/message_util.js b/static/js/message_util.js
index ae130e15bb..717d8af961 100644
--- a/static/js/message_util.js
+++ b/static/js/message_util.js
@@ -78,4 +78,23 @@ exports.get_max_message_id_in_stream = function (stream_id) {
     return max_message_id;
 };
 
+exports.get_topics_for_message_ids = function (message_ids) {
+    const topics = new Map(); // key = stream_id:topic
+    for (const msg_id of message_ids) {
+        // message_store still has data on deleted messages when this runs.
+        const message = message_store.get(msg_id);
+        if (message === undefined) {
+            // We may not have the deleted message cached locally in
+            // message_store; if so, we can just skip processing it.
+            continue;
+        }
+        if (message.type === "stream") {
+            // Create unique keys for stream_id and topic.
+            const topic_key = message.stream_id + ":" + message.topic;
+            topics.set(topic_key, [message.stream_id, message.topic]);
+        }
+    }
+    return topics;
+};
+
 window.message_util = exports;
diff --git a/static/js/recent_senders.js b/static/js/recent_senders.js
index 1d95ca7751..4880ecc264 100644
--- a/static/js/recent_senders.js
+++ b/static/js/recent_senders.js
@@ -74,21 +74,7 @@ exports.process_topic_edit = function (old_stream_id, old_topic, new_topic, new_
 };
 
 exports.update_topics_of_deleted_message_ids = function (message_ids) {
-    const topics_to_update = new Map();
-    for (const msg_id of message_ids) {
-        // message_store still has data on deleted messages when this runs.
-        const message = message_store.get(msg_id);
-        if (message === undefined) {
-            // We may not have the deleted message cached locally in
-            // message_store; if so, we can just skip processing it.
-            continue;
-        }
-        if (message.type === "stream") {
-            // Create unique keys for stream_id and topic.
-            const topic_key = message.stream_id + ":" + message.topic;
-            topics_to_update.set(topic_key, [message.stream_id, message.topic]);
-        }
-    }
+    const topics_to_update = message_util.get_topics_for_message_ids(message_ids);
 
     for (const [stream_id, topic] of topics_to_update.values()) {
         const topic_dict = topic_senders.get(stream_id);
diff --git a/static/js/recent_topics.js b/static/js/recent_topics.js
index 1681fd5a1f..12a7dd6b9a 100644
--- a/static/js/recent_topics.js
+++ b/static/js/recent_topics.js
@@ -237,19 +237,7 @@ exports.topic_in_search_results = function (keyword, stream, topic) {
 };
 
 exports.update_topics_of_deleted_message_ids = function (message_ids) {
-    const topics_to_rerender = new Map();
-    for (const msg_id of message_ids) {
-        const message = message_store.get(msg_id);
-        if (message === undefined) {
-            // We may not have the deleted message cached locally in
-            // message_store; if so, we can just skip processing it.
-            continue;
-        }
-        if (message.type === "stream") {
-            const topic_key = get_topic_key(message.stream_id, message.topic);
-            topics_to_rerender.set(topic_key, [message.stream_id, message.topic]);
-        }
-    }
+    const topics_to_rerender = message_util.get_topics_for_message_ids(message_ids);
 
     for (const [stream_id, topic] of topics_to_rerender.values()) {
         topics.delete(get_topic_key(stream_id, topic));