diff --git a/static/js/stream_topic_history.js b/static/js/stream_topic_history.js
index a7aaa419a7..58c3426bd9 100644
--- a/static/js/stream_topic_history.js
+++ b/static/js/stream_topic_history.js
@@ -1,6 +1,6 @@
 const FoldDict = require("./fold_dict").FoldDict;
 
-const stream_dict = new Map(); // stream_id -> per_stream_history object
+const stream_dict = new Map(); // stream_id -> PerStreamHistory object
 const fetched_stream_ids = new Set();
 
 exports.is_complete_for_stream_id = (stream_id) => {
@@ -42,7 +42,7 @@ exports.stream_has_topics = function (stream_id) {
     return history.has_topics();
 };
 
-exports.per_stream_history = function (stream_id) {
+class PerStreamHistory {
     /*
         For a given stream, this structure has a dictionary of topics.
         The main getter of this object is get_recent_topic_names, and
@@ -72,32 +72,35 @@ exports.per_stream_history = function (stream_id) {
           deleted.
     */
 
-    const topics = new FoldDict();
+    topics = new FoldDict();
     // Most recent message ID for the stream.
-    let max_message_id = 0;
-    const self = {};
+    max_message_id = 0;
 
-    self.has_topics = function () {
-        return topics.size !== 0;
-    };
+    constructor(stream_id) {
+        this.stream_id = stream_id;
+    }
 
-    self.update_stream_max_message_id = function (message_id) {
-        if (message_id > max_message_id) {
-            max_message_id = message_id;
+    has_topics() {
+        return this.topics.size !== 0;
+    }
+
+    update_stream_max_message_id(message_id) {
+        if (message_id > this.max_message_id) {
+            this.max_message_id = message_id;
         }
-    };
+    }
 
-    self.add_or_update = function (opts) {
+    add_or_update(opts) {
         const topic_name = opts.topic_name;
         let message_id = opts.message_id || 0;
 
         message_id = parseInt(message_id, 10);
-        self.update_stream_max_message_id(message_id);
+        this.update_stream_max_message_id(message_id);
 
-        const existing = topics.get(topic_name);
+        const existing = this.topics.get(topic_name);
 
         if (!existing) {
-            topics.set(opts.topic_name, {
+            this.topics.set(opts.topic_name, {
                 message_id,
                 pretty_name: topic_name,
                 historical: false,
@@ -114,10 +117,10 @@ exports.per_stream_history = function (stream_id) {
             existing.message_id = message_id;
             existing.pretty_name = topic_name;
         }
-    };
+    }
 
-    self.maybe_remove = function (topic_name, num_messages) {
-        const existing = topics.get(topic_name);
+    maybe_remove(topic_name, num_messages) {
+        const existing = this.topics.get(topic_name);
 
         if (!existing) {
             return;
@@ -131,14 +134,14 @@ exports.per_stream_history = function (stream_id) {
         }
 
         if (existing.count <= num_messages) {
-            topics.delete(topic_name);
+            this.topics.delete(topic_name);
             return;
         }
 
         existing.count -= num_messages;
-    };
+    }
 
-    self.add_history = function (server_history) {
+    add_history(server_history) {
         // This method populates historical topics from the
         // server.  We have less data about these than the
         // client can maintain for newer topics.
@@ -147,7 +150,7 @@ exports.per_stream_history = function (stream_id) {
             const topic_name = obj.name;
             const message_id = obj.max_id;
 
-            const existing = topics.get(topic_name);
+            const existing = this.topics.get(topic_name);
 
             if (existing) {
                 if (!existing.historical) {
@@ -161,21 +164,21 @@ exports.per_stream_history = function (stream_id) {
             // the topic for the first time, or we are getting
             // more current data for it.
 
-            topics.set(topic_name, {
+            this.topics.set(topic_name, {
                 message_id,
                 pretty_name: topic_name,
                 historical: true,
             });
-            self.update_stream_max_message_id(message_id);
+            this.update_stream_max_message_id(message_id);
         }
-    };
+    }
 
-    self.get_recent_topic_names = function () {
-        const my_recents = Array.from(topics.values());
+    get_recent_topic_names() {
+        const my_recents = Array.from(this.topics.values());
 
         const missing_topics = unread.get_missing_topics({
-            stream_id,
-            topic_dict: topics,
+            stream_id: this.stream_id,
+            topic_dict: this.topics,
         });
 
         const recents = my_recents.concat(missing_topics);
@@ -185,14 +188,13 @@ exports.per_stream_history = function (stream_id) {
         const names = recents.map((obj) => obj.pretty_name);
 
         return names;
-    };
+    }
 
-    self.get_max_message_id = function () {
-        return max_message_id;
-    };
-
-    return self;
-};
+    get_max_message_id() {
+        return this.max_message_id;
+    }
+}
+exports.PerStreamHistory = PerStreamHistory;
 
 exports.remove_messages = function (opts) {
     const stream_id = opts.stream_id;
@@ -215,7 +217,7 @@ exports.find_or_create = function (stream_id) {
     let history = stream_dict.get(stream_id);
 
     if (!history) {
-        history = exports.per_stream_history(stream_id);
+        history = new PerStreamHistory(stream_id);
         stream_dict.set(stream_id, history);
     }