diff --git a/static/js/activity.js b/static/js/activity.js
index 33fbcd5988..3b4cd91103 100644
--- a/static/js/activity.js
+++ b/static/js/activity.js
@@ -41,11 +41,11 @@ function sort_users(users, user_info) {
         // Sort equivalent PM names alphabetically
         var full_name_a = a;
         var full_name_b = b;
-        if (people_dict[a] !== undefined) {
-            full_name_a = people_dict[a].full_name;
+        if (people_dict.has(a)) {
+            full_name_a = people_dict.get(a).full_name;
         }
-        if (people_dict[b] !== undefined) {
-            full_name_b = people_dict[b].full_name;
+        if (people_dict.has(b)) {
+            full_name_b = people_dict.get(b).full_name;
         }
         return util.strcmp(full_name_a, full_name_b);
     });
diff --git a/static/js/composebox_typeahead.js b/static/js/composebox_typeahead.js
index 40ae465545..0509d654f9 100644
--- a/static/js/composebox_typeahead.js
+++ b/static/js/composebox_typeahead.js
@@ -203,8 +203,8 @@ exports.initialize = function () {
     $( "#subject" ).typeahead({
         source: function (query, process) {
             var stream_name = $("#stream").val(), i;
-            if (subject_dict.hasOwnProperty(stream_name)) {
-                return subject_dict[stream_name];
+            if (subject_dict.has(stream_name)) {
+                return subject_dict.get(stream_name);
             }
             return [];
         },
diff --git a/static/js/dict.js b/static/js/dict.js
index 7d9f844991..deb2160cb2 100644
--- a/static/js/dict.js
+++ b/static/js/dict.js
@@ -33,7 +33,7 @@ function unmunge(k) {
     return k.substr(1);
 }
 
-Dict.prototype = {
+Dict.prototype = _.object(_.map({
     get: function Dict_get(key) {
         return this._items[munge(key)];
     },
@@ -63,12 +63,9 @@ Dict.prototype = {
             return [unmunge(pair[0]), pair[1]];
         });
     }
-};
-
-Dict.prototype = _.object(_.map(Dict.prototype,
-                                function (value, key) {
-                                    return [key, util.enforce_arity(value)];
-                                }));
+}, function (value, key) {
+    return [key, util.enforce_arity(value)];
+}));
 
 }());
 
diff --git a/static/js/narrow.js b/static/js/narrow.js
index 2c61b51f3b..4d808c3168 100644
--- a/static/js/narrow.js
+++ b/static/js/narrow.js
@@ -291,15 +291,15 @@ exports.search_string = function () {
 // Collect operators which appear only once into an object,
 // and discard those which appear more than once.
 function collect_single(operators) {
-    var seen   = {};
-    var result = {};
+    var seen   = new Dict();
+    var result = new Dict();
     _.each(operators, function (elem) {
         var key = elem[0];
-        if (seen.hasOwnProperty(key)) {
-            delete result[key];
+        if (seen.has(key)) {
+            result.del(key);
         } else {
-            result[key] = elem[1];
-            seen  [key] = true;
+            result.set(key, elem[1]);
+            seen.set(key, true);
         }
     });
     return result;
@@ -317,16 +317,16 @@ exports.set_compose_defaults = function (opts) {
     // Set the stream, subject, and/or PM recipient if they are
     // uniquely specified in the narrow view.
 
-    if (single.stream) {
-        opts.stream = single.stream;
+    if (single.has('stream')) {
+        opts.stream = single.get('stream');
     }
 
-    if (single.topic) {
-        opts.subject = single.topic;
+    if (single.has('topic')) {
+        opts.subject = single.get('topic');
     }
 
-    if (single['pm-with'] !== undefined) {
-        opts.private_message_recipient = single['pm-with'];
+    if (single.has('pm-with')) {
+        opts.private_message_recipient = single.get('pm-with');
     }
 };
 
diff --git a/static/js/search_suggestion.js b/static/js/search_suggestion.js
index 4982e50ec5..caaef59e3b 100644
--- a/static/js/search_suggestion.js
+++ b/static/js/search_suggestion.js
@@ -281,7 +281,7 @@ function get_topic_suggestions(query_operators) {
 
     stream = subs.canonicalized_name(stream);
 
-    var topics = recent_subjects[stream];
+    var topics = recent_subjects.get(stream);
 
     if (!topics) {
         return [];
diff --git a/static/js/stream_list.js b/static/js/stream_list.js
index bfc772930f..e20db05f7d 100644
--- a/static/js/stream_list.js
+++ b/static/js/stream_list.js
@@ -16,11 +16,9 @@ exports.sort_narrow_list = function () {
 
     streams.sort(function (a, b) {
         if (sort_recent) {
-            if (recent_subjects[b] !== undefined &&
-                recent_subjects[a] === undefined) {
+            if (recent_subjects.has(b) && ! recent_subjects.has(a)) {
                 return 1;
-            } else if (recent_subjects[b] === undefined &&
-                       recent_subjects[a] !== undefined) {
+            } else if (! recent_subjects.has(b) && recent_subjects.has(a)) {
                 return -1;
             }
         }
@@ -41,7 +39,7 @@ exports.sort_narrow_list = function () {
     _.each(streams, function (stream) {
         var li = $(subs.get(stream).sidebar_li);
         if (sort_recent) {
-            if (recent_subjects[stream] === undefined) {
+            if (! recent_subjects.has(stream)) {
                 li.addClass('inactive_stream');
             } else {
                 li.removeClass('inactive_stream');
@@ -152,7 +150,7 @@ function rebuild_recent_subjects(stream, subject) {
     $('.expanded_subjects').remove();
     var max_subjects = 5;
     var stream_li = get_filter_li('stream', stream);
-    var subjects = recent_subjects[stream] || [];
+    var subjects = recent_subjects.get(stream) || [];
     var active_orig_subject = subject;
     var display_subjects = _.filter(subjects, function (subject_obj, idx) {
         var num_unread = unread.num_unread_for_subject(stream, subject_obj.canon_subject);
@@ -230,19 +228,27 @@ exports.update_dom_with_unread_counts = function (counts) {
     // Our job is to update some DOM elements.
 
     // counts.stream_count maps streams to counts
-    _.each(counts.stream_count, function (count, stream) {
+    _.each(counts.stream_count.items(), function (item) {
+        var stream = item[0];
+        var count = item[1];
         exports.set_count("stream", stream, count);
     });
 
     // counts.subject_count maps streams to hashes of subjects to counts
-    _.each(counts.subject_count, function (subject_hash, stream) {
-        _.each(subject_hash, function (count, subject) {
+    _.each(counts.subject_count.items(), function (item) {
+        var stream = item[0];
+        var subject_hash = item[1];
+        _.each(subject_hash.items(), function (item) {
+            var subject = item[0];
+            var count = item[1];
             exports.set_subject_count(stream, subject, count);
         });
     });
 
     // counts.pm_count maps people to counts
-    _.each(counts.pm_count, function (count, person) {
+    _.each(counts.pm_count.items(), function (item) {
+        var person = item[0];
+        var count = item[1];
         exports.set_count("private", person, count);
     });
 
diff --git a/static/js/subs.js b/static/js/subs.js
index a763d492ac..41eeb24c5c 100644
--- a/static/js/subs.js
+++ b/static/js/subs.js
@@ -2,16 +2,16 @@ var subs = (function () {
 
 var exports = {};
 
-var stream_info = {}; // Maps lowercase stream name to stream properties object
+var stream_info = new Dict(); // Maps lowercase stream name to stream properties object
 
 var next_sub_id = 0;
 
 function add_sub(stream_name, sub) {
-    stream_info[stream_name.toLowerCase()] = sub;
+    stream_info.set(stream_name.toLowerCase(), sub);
 }
 
 function get_sub(stream_name) {
-    return stream_info[stream_name.toLowerCase()];
+    return stream_info.get(stream_name.toLowerCase());
 }
 
 exports.stream_info = function (new_stream_info) {
@@ -23,8 +23,7 @@ exports.stream_info = function (new_stream_info) {
 };
 
 exports.subscribed_streams = function () {
-    return _.chain(stream_info)
-        .values()
+    return _.chain(stream_info.values())
         .where({subscribed: true})
         .pluck('name')
         .value();
@@ -43,7 +42,7 @@ exports.update_all_messages_link = function () {
     // the user has any subscriptions hidden from home view.
     var all_messages = $("#global_filters [data-name='all']")[0];
 
-    if (_.every(stream_info, function (sub) { return sub.in_home_view; })) {
+    if (_.every(stream_info.values(), function (sub) { return sub.in_home_view; })) {
         $(all_messages).addClass('hidden-filter');
     } else {
         $(all_messages).removeClass('hidden-filter');
@@ -385,7 +384,7 @@ exports.reload_subscriptions = function (opts) {
     }
 
     if (opts.clear_first) {
-        stream_info = {};
+        stream_info = new Dict();
         stream_list.remove_all_narrow_filters();
     }
 
@@ -739,7 +738,7 @@ $(function () {
                         // mark_subscribed adds the user to the member list
                         mark_subscribed(stream);
                     } else {
-                        add_to_member_list(list, people_dict[principal].full_name, principal);
+                        add_to_member_list(list, people_dict.get(principal).full_name, principal);
                     }
                 } else {
                     error_elem.addClass("hide");
@@ -782,11 +781,11 @@ $(function () {
             success: function (data) {
                 util.destroy_loading_indicator(indicator_elem);
                 var subscribers = _.map(data.subscribers, function (elem) {
-                    var person = people_dict[elem];
+                    var person = people_dict.get(elem);
                     if (person === undefined) {
                         return elem;
                     }
-                    return format_member_list_elem(people_dict[elem].full_name, elem);
+                    return format_member_list_elem(people_dict.get(elem).full_name, elem);
                 });
                 _.each(subscribers.sort().reverse(), function (elem) {
                     // add_to_member_list *prepends* the element,
diff --git a/static/js/tab_bar.js b/static/js/tab_bar.js
index 692c01228b..261ea45c8a 100644
--- a/static/js/tab_bar.js
+++ b/static/js/tab_bar.js
@@ -41,10 +41,10 @@ function make_tab_data() {
             if (filter.has_operator("pm-with")) {
                 var emails = filter.operands("pm-with")[0].split(',');
                 var names = _.map(emails, function (email) {
-                    if (! people_dict[email]) {
+                    if (! people_dict.has(email)) {
                         return email;
                     }
-                    return people_dict[email].full_name;
+                    return people_dict.get(email).full_name;
                 });
 
                 tabs.push(make_tab(names.join(', '), hashed));
@@ -60,8 +60,8 @@ function make_tab_data() {
             tabs.push(make_tab("Mentions", hashed));
         } else if (filter.has_operator("sender")) {
             var sender = filter.operands("sender")[0];
-            if (people_dict[sender]) {
-                sender = people_dict[sender].full_name;
+            if (people_dict.has(sender)) {
+                sender = people_dict.get(sender).full_name;
             }
             tabs.push(make_tab("Sent by " + sender, hashed));
         }  else if (filter.has_operator("search")) {
diff --git a/static/js/tutorial.js b/static/js/tutorial.js
index c4f3ed6973..e967b62126 100644
--- a/static/js/tutorial.js
+++ b/static/js/tutorial.js
@@ -7,9 +7,9 @@ var event_handlers = {};
 // We'll temporarily set stream colors for the streams we use in the demo
 // tutorial messages.
 var real_stream_info;
-var tutorial_stream_info = {"design": {"color": "#76ce90"},
-                            "social": {"color": "#fae589"},
-                            "devel": {"color": "#a6c7e5"}};
+var tutorial_stream_info = new Dict({"design": {"color": "#76ce90"},
+                                     "social": {"color": "#fae589"},
+                                     "devel": {"color": "#a6c7e5"}});
 
 // Each message object contains the minimal information necessary for it to be
 // processed by our system for adding messages to your feed.
diff --git a/static/js/ui.js b/static/js/ui.js
index 86a9fabf4f..c7519e917b 100644
--- a/static/js/ui.js
+++ b/static/js/ui.js
@@ -1434,7 +1434,7 @@ exports.set_presence_list = function (users, presence_info) {
     function info_for(email) {
         var presence = presence_info[email];
         return {
-            name: people_dict[email].full_name,
+            name: people_dict.get(email).full_name,
             email: email,
             type: presence,
             type_desc: presence_descriptions[presence]
@@ -1442,7 +1442,7 @@ exports.set_presence_list = function (users, presence_info) {
     }
 
     var user_emails = _.filter(users, function (email) {
-        return people_dict[email] !== undefined;
+        return people_dict.has(email);
     });
 
     var user_info = [my_info].concat(_.map(user_emails, info_for));
diff --git a/static/js/unread.js b/static/js/unread.js
index f5f8ba3a44..37bf386c17 100644
--- a/static/js/unread.js
+++ b/static/js/unread.js
@@ -3,11 +3,11 @@ var unread = (function () {
 var exports = {};
 
 var unread_counts = {
-    'stream': {},
-    'private': {}
+    'stream': new Dict(),
+    'private': new Dict()
 };
 var unread_mentioned = {};
-var unread_subjects = {};
+var unread_subjects = new Dict();
 
 function unread_hashkey(message) {
     var hashkey;
@@ -17,17 +17,17 @@ function unread_hashkey(message) {
         hashkey = message.reply_to;
     }
 
-    if (unread_counts[message.type][hashkey] === undefined) {
-        unread_counts[message.type][hashkey] = {};
+    if (! unread_counts[message.type].has(hashkey)) {
+        unread_counts[message.type].set(hashkey, {});
     }
 
     if (message.type === 'stream') {
         var canon_subject = subs.canonicalized_name(message.subject);
-        if (unread_subjects[hashkey] === undefined) {
-            unread_subjects[hashkey] = {};
+        if (! unread_subjects.has(hashkey)) {
+            unread_subjects.set(hashkey, new Dict());
         }
-        if (unread_subjects[hashkey][canon_subject] === undefined) {
-            unread_subjects[hashkey][canon_subject] = {};
+        if (! unread_subjects.get(hashkey).has(canon_subject)) {
+            unread_subjects.get(hashkey).set(canon_subject, {});
         }
     }
 
@@ -47,19 +47,19 @@ exports.update_unread_subjects = function (msg, event) {
     var canon_subject = subs.canonicalized_name(msg.subject);
 
     if (event.subject !== undefined &&
-        unread_subjects[canon_stream] !== undefined &&
-        unread_subjects[canon_stream][canon_subject] !== undefined &&
-        unread_subjects[canon_stream][canon_subject][msg.id]) {
+        unread_subjects.has(canon_stream) &&
+        unread_subjects.get(canon_stream).has(canon_subject) &&
+        unread_subjects.get(canon_stream).get(canon_subject)[msg.id]) {
         var new_canon_subject = subs.canonicalized_name(event.subject);
         // Move the unread subject count to the new subject
-        delete unread_subjects[canon_stream][canon_subject][msg.id];
-        if (unread_subjects[canon_stream][canon_subject].length === 0) {
-            delete unread_subjects[canon_stream][canon_subject];
+        delete unread_subjects.get(canon_stream).get(canon_subject)[msg.id];
+        if (unread_subjects.get(canon_stream).get(canon_subject).length === 0) {
+            unread_subjects.get(canon_stream).del(canon_subject);
         }
-        if (unread_subjects[canon_stream][new_canon_subject] === undefined) {
-            unread_subjects[canon_stream][new_canon_subject] = {};
+        if (! unread_subjects.get(canon_stream).has(new_canon_subject)) {
+            unread_subjects.get(canon_stream).set(new_canon_subject, {});
         }
-        unread_subjects[canon_stream][new_canon_subject][msg.id] = true;
+        unread_subjects.get(canon_stream).get(new_canon_subject)[msg.id] = true;
     }
 };
 
@@ -71,11 +71,11 @@ exports.process_loaded_messages = function (messages) {
         }
 
         var hashkey = unread_hashkey(message);
-        unread_counts[message.type][hashkey][message.id] = true;
+        unread_counts[message.type].get(hashkey)[message.id] = true;
 
         if (message.type === 'stream') {
             var canon_subject = subs.canonicalized_name(message.subject);
-            unread_subjects[hashkey][canon_subject][message.id] = true;
+            unread_subjects.get(hashkey).get(canon_subject)[message.id] = true;
         }
 
         if (message.mentioned) {
@@ -86,17 +86,17 @@ exports.process_loaded_messages = function (messages) {
 
 exports.process_read_message = function (message) {
     var hashkey = unread_hashkey(message);
-    delete unread_counts[message.type][hashkey][message.id];
+    delete unread_counts[message.type].get(hashkey)[message.id];
     if (message.type === 'stream') {
         var canon_stream = subs.canonicalized_name(message.stream);
         var canon_subject = subs.canonicalized_name(message.subject);
-        delete unread_subjects[canon_stream][canon_subject][message.id];
+        delete unread_subjects.get(canon_stream).get(canon_subject)[message.id];
     }
     delete unread_mentioned[message.id];
 };
 
 exports.declare_bankruptcy = function () {
-    unread_counts = {'stream': {}, 'private': {}};
+    unread_counts = {'stream': new Dict(), 'private': new Dict()};
 };
 
 exports.num_unread_current_messages = function () {
@@ -120,9 +120,9 @@ exports.get_counts = function () {
     res.private_message_count = 0;
     res.home_unread_messages = 0;
     res.mentioned_message_count = Object.keys(unread_mentioned).length;
-    res.stream_count = {};  // hash by stream -> count
-    res.subject_count = {}; // hash of hashes (stream, then subject -> count)
-    res.pm_count = {}; // Hash by email -> count
+    res.stream_count = new Dict();  // hash by stream -> count
+    res.subject_count = new Dict(); // hash of hashes (stream, then subject -> count)
+    res.pm_count = new Dict(); // Hash by email -> count
 
     function only_in_home_view(msgids) {
         return _.filter(msgids, function (msgid) {
@@ -130,31 +130,37 @@ exports.get_counts = function () {
         });
     }
 
-    _.each(unread_counts.stream, function (msgs, stream) {
+    _.each(unread_counts.stream.items(), function (item) {
+        var stream = item[0];
+        var msgs = item[1];
         if (! subs.is_subscribed(stream)) {
             return true;
         }
 
         var count = Object.keys(msgs).length;
-        res.stream_count[stream] = count;
+        res.stream_count.set(stream, count);
 
         if (subs.in_home_view(stream)) {
             res.home_unread_messages += only_in_home_view(Object.keys(msgs)).length;
         }
 
-        if (unread_subjects[stream] !== undefined) {
-            res.subject_count[stream] = {};
-            _.each(unread_subjects[stream], function (msgs, subject) {
-                res.subject_count[stream][subject] = Object.keys(msgs).length;
+        if (unread_subjects.has(stream)) {
+            res.subject_count.set(stream, new Dict());
+            _.each(unread_subjects.get(stream).items(), function (item) {
+                var subject = item[0];
+                var msgs = item[1];
+                res.subject_count.get(stream).set(subject, Object.keys(msgs).length);
             });
         }
 
     });
 
     var pm_count = 0;
-    _.each(unread_counts["private"], function (obj, index) {
+    _.each(unread_counts["private"].items(), function (item) {
+        var index = item[0];
+        var obj = item[1];
         var count = Object.keys(obj).length;
-        res.pm_count[index] = count;
+        res.pm_count.set(index, count);
         pm_count += count;
     });
     res.private_message_count = pm_count;
@@ -172,9 +178,9 @@ exports.get_counts = function () {
 
 exports.num_unread_for_subject = function (stream, subject) {
     var num_unread = 0;
-    if (unread_subjects[stream] !== undefined &&
-        unread_subjects[stream][subject] !== undefined) {
-        num_unread = Object.keys(unread_subjects[stream][subject]).length;
+    if (unread_subjects.has(stream) &&
+        unread_subjects.get(stream).has(subject)) {
+        num_unread = Object.keys(unread_subjects.get(stream).get(subject)).length;
     }
     return num_unread;
 };
diff --git a/static/js/zulip.js b/static/js/zulip.js
index c4e54b2f82..0480f91746 100644
--- a/static/js/zulip.js
+++ b/static/js/zulip.js
@@ -5,9 +5,9 @@ var home_msg_list = new MessageList('zhome',
 );
 var narrowed_msg_list;
 var current_msg_list = home_msg_list;
-var subject_dict = {};
-var people_dict = {};
-var recent_subjects = {};
+var subject_dict = new Dict();
+var people_dict = new Dict();
+var recent_subjects = new Dict();
 
 var queued_mark_as_read = [];
 var queued_flag_timer;
@@ -43,7 +43,7 @@ var waiting_on_browser_scroll = true;
 
 function add_person(person) {
     page_params.people_list.push(person);
-    people_dict[person.email] = person;
+    people_dict.set(person.email, person);
     person.pm_recipient_count = 0;
 }
 
@@ -55,7 +55,7 @@ function remove_person(person) {
             break;
         }
     }
-    delete people_dict[person.email];
+    people_dict.del(person.email);
 }
 
 function update_person(person) {
@@ -64,12 +64,12 @@ function update_person(person) {
     // that can change, this will need to either get complicated or be
     // replaced by MVC
     var i;
-    if (people_dict[person.email] === undefined) {
+    if (! people_dict.has(person.email)) {
         blueslip.error("Got update_person event for unexpected user",
                        {email: person.email});
         return;
     }
-    people_dict[person.email].full_name = person.full_name;
+    people_dict.get(person.email).full_name = person.full_name;
     for (i = 0; i < page_params.people_list.length; i++) {
         if (page_params.people_list[i].email === person.email) {
             page_params.people_list[i].full_name = person.full_name;
@@ -503,22 +503,22 @@ function process_message_for_recent_subjects(message, remove_message) {
     var canon_stream = subs.canonicalized_name(message.stream);
     var canon_subject = subs.canonicalized_name(message.subject);
 
-    if (! recent_subjects.hasOwnProperty(canon_stream)) {
-        recent_subjects[canon_stream] = [];
+    if (! recent_subjects.has(canon_stream)) {
+        recent_subjects.set(canon_stream, []);
     } else {
-        recent_subjects[canon_stream] =
-            _.filter(recent_subjects[canon_stream], function (item) {
-                var is_duplicate = (item.canon_subject.toLowerCase() === canon_subject.toLowerCase());
-                if (is_duplicate) {
-                    current_timestamp = item.timestamp;
-                    count = item.count;
-                }
+        recent_subjects.set(canon_stream,
+                            _.filter(recent_subjects.get(canon_stream), function (item) {
+                                var is_duplicate = (item.canon_subject.toLowerCase() === canon_subject.toLowerCase());
+                                if (is_duplicate) {
+                                    current_timestamp = item.timestamp;
+                                    count = item.count;
+                                }
 
-                return !is_duplicate;
-            });
+                                return !is_duplicate;
+                            }));
     }
 
-    var recents = recent_subjects[canon_stream];
+    var recents = recent_subjects.get(canon_stream);
 
     if (remove_message !== undefined) {
         count = count - 1;
@@ -537,7 +537,7 @@ function process_message_for_recent_subjects(message, remove_message) {
         return b.timestamp - a.timestamp;
     });
 
-    recent_subjects[canon_stream] = recents;
+    recent_subjects.set(canon_stream, recents);
 }
 
 var msg_metadata_cache = {};
@@ -570,12 +570,12 @@ function add_message_metadata(message) {
     case 'stream':
         message.is_stream = true;
         message.stream = message.display_recipient;
-        if (! _.has(subject_dict, message.stream)) {
-            subject_dict[message.stream] = [];
+        if (! subject_dict.has(message.stream)) {
+            subject_dict.set(message.stream, []);
         }
-        if (! case_insensitive_find(message.subject, subject_dict[message.stream])) {
-            subject_dict[message.stream].push(message.subject);
-            subject_dict[message.stream].sort();
+        if (! case_insensitive_find(message.subject, subject_dict.get(message.stream))) {
+            subject_dict.get(message.stream).push(message.subject);
+            subject_dict.get(message.stream).sort();
         }
         message.reply_to = message.sender_email;
 
@@ -608,13 +608,13 @@ function add_message_metadata(message) {
     _.each(involved_people, function (person) {
         // Do the hasOwnProperty() call via the prototype to avoid problems
         // with keys like "hasOwnProperty"
-        if (people_dict[person.email] === undefined) {
+        if (! people_dict.has(person.email)) {
             add_person(person);
         }
 
         if (message.type === 'private' && message.sent_by_me) {
             // Track the number of PMs we've sent to this person to improve autocomplete
-            people_dict[person.email].pm_recipient_count += 1;
+            people_dict.get(person.email).pm_recipient_count += 1;
         }
     });
 
@@ -1199,13 +1199,13 @@ function fast_forward_pointer() {
 
 function main() {
     _.each(page_params.people_list, function (person) {
-        people_dict[person.email] = person;
+        people_dict.set(person.email, person);
         person.pm_recipient_count = 0;
     });
 
     // The special account feedback@zulip.com is used for in-app
     // feedback and should always show up as an autocomplete option.
-    if (people_dict['feedback@zulip.com'] === undefined){
+    if (! people_dict.has('feedback@zulip.com')){
         add_person({"email": "feedback@zulip.com",
                     "full_name": "Zulip Feedback Bot"});
     }
diff --git a/zerver/tests/frontend/node/activity.js b/zerver/tests/frontend/node/activity.js
index 3820f704b1..185f4b1da8 100644
--- a/zerver/tests/frontend/node/activity.js
+++ b/zerver/tests/frontend/node/activity.js
@@ -4,6 +4,7 @@ var assert = require('assert');
     global._ = require('third/underscore/underscore.js');
     global.activity = require('js/activity.js');
     global.util = require('js/util.js');
+    global.Dict = require('js/dict.js');
 }());
 
 var activity = global.activity;
@@ -18,11 +19,11 @@ var activity = global.activity;
     };
 
 
-    global.people_dict = {
+    global.people_dict = new global.Dict({
         'alice@zulip.com': 'Alice Smith',
         'fred@zulip.com': 'Fred Flintstone',
         'jill@zulip.com': 'Jill Hill'
-    };
+    });
 
     activity._sort_users(users, user_info);
 
diff --git a/zerver/tests/frontend/node/filter.js b/zerver/tests/frontend/node/filter.js
index 1cce023602..bb045042b4 100644
--- a/zerver/tests/frontend/node/filter.js
+++ b/zerver/tests/frontend/node/filter.js
@@ -3,6 +3,8 @@ var assert = require('assert');
 (function set_up_dependencies () {
     global._ = require('third/underscore/underscore.js');
 
+    global.util = require('js/util.js');
+    global.Dict = require('js/dict.js');
     // An upcoming change is to put Filter in its own module, but
     // for now it still lives in narrow.js.  (I'm waiting for a big
     // commit from Zev to hit master first.  Once that happens,
diff --git a/zerver/tests/frontend/node/narrow.js b/zerver/tests/frontend/node/narrow.js
index 35ecda4391..32d975804c 100644
--- a/zerver/tests/frontend/node/narrow.js
+++ b/zerver/tests/frontend/node/narrow.js
@@ -3,6 +3,7 @@ var assert = require('assert');
 (function set_up_dependencies () {
     global._ = require('third/underscore/underscore.js');
     global.util = require('js/util.js');
+    global.Dict = require('js/dict.js');
     global.narrow = require('js/narrow.js');
     global.$ = function () {}; // for subs.js
     global.subs = require('js/subs.js');
diff --git a/zerver/tests/frontend/node/search_suggestion.js b/zerver/tests/frontend/node/search_suggestion.js
index 29af6d92ab..b40759cc1e 100644
--- a/zerver/tests/frontend/node/search_suggestion.js
+++ b/zerver/tests/frontend/node/search_suggestion.js
@@ -31,9 +31,9 @@ function set_up_dependencies() {
 
     global.typeahead_helper = require('js/typeahead_helper.js');
 
-    global.recent_subjects = {};
-
     global.util = require('js/util.js');
+    global.Dict = require('js/dict.js');
+    global.recent_subjects = new global.Dict();
 
     return search;
 }
@@ -107,13 +107,13 @@ var search = set_up_dependencies();
         return 'office';
     };
 
-    global.recent_subjects = {
+    global.recent_subjects = new global.Dict({
         office: [
             {subject: 'team'},
             {subject: 'ignore'},
             {subject: 'test'}
         ]
-    };
+    });
 
     var suggestions = search.get_suggestions(query);
 
@@ -144,7 +144,7 @@ var search = set_up_dependencies();
         return;
     };
 
-    global.recent_subjects = {};
+    global.recent_subjects = new global.Dict();
 
     var suggestions = search.get_suggestions(query);
 
@@ -177,13 +177,13 @@ var search = set_up_dependencies();
         }
     ];
 
-    global.recent_subjects = {
+    global.recent_subjects = new global.Dict({
         office: [
             {subject: 'team'},
             {subject: 'ignore'},
             {subject: 'test'}
         ]
-    };
+    });
 
     var suggestions = search.get_suggestions(query);
 
diff --git a/zerver/tests/frontend/node/unread.js b/zerver/tests/frontend/node/unread.js
index aa4ba171fe..1e987b31a4 100644
--- a/zerver/tests/frontend/node/unread.js
+++ b/zerver/tests/frontend/node/unread.js
@@ -8,6 +8,9 @@
 // dependencies (except _).
 
 global._ = require('third/underscore/underscore.js');
+global.util = require('js/util.js');
+global.Dict = require('js/dict.js');
+var Dict = global.Dict;
 var unread = require('js/unread.js');
 var assert = require('assert');
 
@@ -31,9 +34,9 @@ var zero_counts = {
     private_message_count: 0,
     home_unread_messages: 0,
     mentioned_message_count: 0,
-    stream_count: {},
-    subject_count: {},
-    pm_count: {},
+    stream_count: new Dict(),
+    subject_count: new Dict(),
+    pm_count: new Dict(),
     unread_in_current_view: 0
 };