diff --git a/.eslintrc.json b/.eslintrc.json
index 563180173d..d671a56eba 100644
--- a/.eslintrc.json
+++ b/.eslintrc.json
@@ -36,6 +36,7 @@
         "resize": false,
         "loading": false,
         "typing": false,
+        "typing_data": false,
         "compose": false,
         "compose_actions": false,
         "compose_state": false,
diff --git a/frontend_tests/node_tests/typing_data.js b/frontend_tests/node_tests/typing_data.js
new file mode 100644
index 0000000000..bee4541b7c
--- /dev/null
+++ b/frontend_tests/node_tests/typing_data.js
@@ -0,0 +1,47 @@
+var typing_data = require("js/typing_data.js");
+
+
+(function test_basics() {
+    // The typing_data needs to be robust with lists of
+    // user ids being in arbitrary sorting order and
+    // possibly in string form instead of integer. So all
+    // the apparent randomness in these tests has a purpose.
+    typing_data.add_typist([5, 10, 15], 15);
+    assert.deepEqual(typing_data.get_group_typists([15, 10, 5]), [15]);
+
+    // test that you can add twice
+    typing_data.add_typist([5, 10, 15], 15);
+
+    // add another id to our first group
+    typing_data.add_typist([5, 10, 15], "10");
+    assert.deepEqual(typing_data.get_group_typists([10, 15, 5]), [10, 15]);
+
+    // start adding to a new group
+    typing_data.add_typist([7, 15], 7);
+    typing_data.add_typist([7, "15"], 15);
+
+    // test get_all_typists
+    assert.deepEqual(typing_data.get_all_typists(), [7, 10, 15]);
+
+    // test basic removal
+    assert(typing_data.remove_typist([15, 7], "7"));
+    assert.deepEqual(typing_data.get_group_typists([7, 15]), [15]);
+
+    // test removing an id that is not there
+    assert(!typing_data.remove_typist([15, 7], 7));
+    assert.deepEqual(typing_data.get_group_typists([7, 15]), [15]);
+    assert.deepEqual(typing_data.get_all_typists(), [10, 15]);
+
+    // remove user from one group, but "15" will still be among
+    // "all typists"
+    assert(typing_data.remove_typist(["15", 7], "15"));
+    assert.deepEqual(typing_data.get_all_typists(), [10, 15]);
+
+    // now remove from the other group
+    assert(typing_data.remove_typist([5, 15, 10], 15));
+    assert.deepEqual(typing_data.get_all_typists(), [10]);
+
+    // test duplicate ids in a groups
+    typing_data.add_typist([20, 40, 20], 20);
+    assert.deepEqual(typing_data.get_group_typists([20, 40]), [20]);
+}());
diff --git a/static/js/typing_data.js b/static/js/typing_data.js
new file mode 100644
index 0000000000..d02cb1f216
--- /dev/null
+++ b/static/js/typing_data.js
@@ -0,0 +1,71 @@
+var typing_data = (function () {
+var exports = {};
+
+var typist_dct = new Dict();
+
+function to_int(s) {
+    return parseInt(s, 10);
+}
+
+function sorted(user_ids) {
+    // This mapping makes sure we are using ints, and
+    // it also makes sure we don't mutate the list.
+    var id_list = _.map(user_ids, to_int);
+    id_list.sort(function (a, b) {
+        return a - b;
+    });
+    id_list = _.uniq(id_list, true);
+
+    return id_list;
+}
+
+function get_key(group) {
+    var ids = sorted(group);
+    return ids.join(',');
+}
+
+exports.add_typist = function (group, typist) {
+    var key = get_key(group);
+    var current = typist_dct.get(key) || [];
+    typist = to_int(typist);
+    if (!_.contains(current, typist)) {
+        current.push(typist);
+    }
+    typist_dct.set(key, sorted(current));
+};
+
+exports.remove_typist = function (group, typist) {
+    var key = get_key(group);
+    var current = typist_dct.get(key) || [];
+
+    typist = to_int(typist);
+    if (!_.contains(current, typist)) {
+        return false;
+    }
+
+    current = _.reject(current, function (user_id) {
+        return to_int(user_id) === to_int(typist);
+    });
+
+    typist_dct.set(key, current);
+    return true;
+};
+
+exports.get_group_typists = function (group) {
+    var key = get_key(group);
+    return typist_dct.get(key) || [];
+};
+
+exports.get_all_typists = function () {
+    var typists = _.flatten(typist_dct.values(), true);
+    typists = sorted(typists);
+    typists = _.uniq(typists, true);
+    return typists;
+};
+
+return exports;
+}());
+
+if (typeof module !== 'undefined') {
+    module.exports = typing_data;
+}
diff --git a/zproject/settings.py b/zproject/settings.py
index 6e40406da9..70f3e64624 100644
--- a/zproject/settings.py
+++ b/zproject/settings.py
@@ -902,6 +902,7 @@ JS_SPECS = {
             'js/bot_data.js',
             'js/reactions.js',
             'js/typing.js',
+            'js/typing_data.js',
             'js/ui_init.js',
             'js/shim.js',
             # JS bundled by webpack is also included here if PIPELINE_ENABLED setting is true