diff --git a/frontend_tests/node_tests/topic_generator.js b/frontend_tests/node_tests/topic_generator.js
index 2814822f9e..4a8b26350e 100644
--- a/frontend_tests/node_tests/topic_generator.js
+++ b/frontend_tests/node_tests/topic_generator.js
@@ -61,6 +61,13 @@ function is_odd(i) { return i % 2 === 1; }
     assert.equal(gen.next(), undefined);
     assert.equal(gen.next(), undefined);
 
+    ints = tg.list_generator([10, 20, 30]);
+
+    function mult10(x) { return x * 10; }
+
+    gen = tg.map(ints, mult10);
+    assert.equal(gen.next(), 100);
+    assert.equal(gen.next(), 200);
 }());
 
 (function test_fchain() {
diff --git a/static/js/topic_generator.js b/static/js/topic_generator.js
index 3e74b2b00c..e6a95d3711 100644
--- a/static/js/topic_generator.js
+++ b/static/js/topic_generator.js
@@ -110,6 +110,18 @@ exports.filter = function (gen, filter_func) {
     };
 };
 
+exports.map = function (gen, map_func) {
+    return {
+        next: function () {
+            var val = gen.next();
+            if (val === undefined) {
+                return;
+            }
+            return map_func(val);
+        },
+    };
+};
+
 exports.next_topic = function (streams, get_topics, has_unread_messages, curr_stream, curr_topic) {
     var stream_gen = exports.wrap(streams, curr_stream);