diff --git a/frontend_tests/node_tests/dict.js b/frontend_tests/node_tests/dict.js
index cbe246bbe1..052b4441f0 100644
--- a/frontend_tests/node_tests/dict.js
+++ b/frontend_tests/node_tests/dict.js
@@ -28,7 +28,7 @@ run_test('basic', () => {
     assert.deepEqual(d.values(), ['baz', 'qux']);
     assert.deepEqual(d.items(), [['foo', 'baz'], ['bar', 'qux']]);
 
-    d.del('bar');
+    d.delete('bar');
     assert.equal(d.has('bar'), false);
     assert.strictEqual(d.get('bar'), undefined);
 
@@ -125,7 +125,7 @@ run_test('num_items', () => {
 
     d.set('bar', 1);
     assert.equal(d.num_items(), 2);
-    d.del('foo');
+    d.delete('foo');
     assert.equal(d.num_items(), 1);
 });
 
diff --git a/frontend_tests/node_tests/fold_dict.js b/frontend_tests/node_tests/fold_dict.js
index 0ef21e8f97..5488b463f3 100644
--- a/frontend_tests/node_tests/fold_dict.js
+++ b/frontend_tests/node_tests/fold_dict.js
@@ -28,7 +28,7 @@ run_test('basic', () => {
     assert.deepEqual(d.values(), ['baz', 'qux']);
     assert.deepEqual(d.items(), [['foo', 'baz'], ['bar', 'qux']]);
 
-    d.del('bar');
+    d.delete('bar');
     assert.equal(d.has('bar'), false);
     assert.strictEqual(d.get('bar'), undefined);
 
@@ -53,7 +53,7 @@ run_test('case insensitivity', () => {
 
     assert.deepEqual(d.keys(), ['fOO']);
 
-    d.del('Foo');
+    d.delete('Foo');
     assert.equal(d.has('foo'), false);
 
     assert.deepEqual(d.keys(), []);
diff --git a/frontend_tests/node_tests/int_dict.js b/frontend_tests/node_tests/int_dict.js
index 33e4d206ef..06c71f4fd8 100644
--- a/frontend_tests/node_tests/int_dict.js
+++ b/frontend_tests/node_tests/int_dict.js
@@ -27,7 +27,7 @@ run_test('basic', () => {
     assert.deepEqual(d.keys(), [101, 102]);
     assert.deepEqual(d.values(), ['baz', 'qux']);
 
-    d.del(102);
+    d.delete(102);
     assert.equal(d.has(102), false);
     assert.strictEqual(d.get(102), undefined);
 
@@ -143,7 +143,7 @@ run_test('num_items', () => {
 
     d.set(102, 1);
     assert.equal(d.num_items(), 2);
-    d.del(101);
+    d.delete(101);
     assert.equal(d.num_items(), 1);
 });
 
diff --git a/static/js/bot_data.js b/static/js/bot_data.js
index c720846d56..58d76b00a1 100644
--- a/static/js/bot_data.js
+++ b/static/js/bot_data.js
@@ -40,8 +40,8 @@ exports.deactivate = function bot_data__deactivate(bot_id) {
 };
 
 exports.del = function bot_data__del(bot_id) {
-    bots.del(bot_id);
-    services.del(bot_id);
+    bots.delete(bot_id);
+    services.delete(bot_id);
     send_change_event();
 };
 
diff --git a/static/js/condense.js b/static/js/condense.js
index 249e8b9c41..ba4d106e55 100644
--- a/static/js/condense.js
+++ b/static/js/condense.js
@@ -148,7 +148,7 @@ exports.clear_message_content_height_cache = function () {
 };
 
 exports.un_cache_message_content_height = function (message_id) {
-    _message_content_height_cache.del(message_id);
+    _message_content_height_cache.delete(message_id);
 };
 
 function get_message_height(elem, message_id) {
diff --git a/static/js/dict.ts b/static/js/dict.ts
index fdd6779334..5f4bb1142c 100644
--- a/static/js/dict.ts
+++ b/static/js/dict.ts
@@ -14,7 +14,7 @@ export class Dict<V> {
         return this._items.has(this._munge(key));
     }
 
-    del(key: string): void {
+    delete(key: string): void {
         this._items.delete(this._munge(key));
     }
 
diff --git a/static/js/fold_dict.ts b/static/js/fold_dict.ts
index e09a61b455..3608da7b1d 100644
--- a/static/js/fold_dict.ts
+++ b/static/js/fold_dict.ts
@@ -34,8 +34,8 @@ export class FoldDict<V> {
         return this._items.has(this._munge(key));
     }
 
-    del(key: string): void {
-        this._items.delete(this._munge(key));
+    delete(key: string): boolean {
+        return this._items.delete(this._munge(key));
     }
 
     keys(): string[] {
diff --git a/static/js/int_dict.ts b/static/js/int_dict.ts
index f8f41ffc6d..62f8cf651a 100644
--- a/static/js/int_dict.ts
+++ b/static/js/int_dict.ts
@@ -37,9 +37,9 @@ export class IntDict<V> {
         return this._map.has(key);
     }
 
-    del(key: number): void {
+    delete(key: number): boolean {
         key = this._convert(key);
-        this._map.delete(key);
+        return this._map.delete(key);
     }
 
     keys(): number[] {
diff --git a/static/js/lazy_set.js b/static/js/lazy_set.js
index b21379b0b6..c6ddce9d0c 100644
--- a/static/js/lazy_set.js
+++ b/static/js/lazy_set.js
@@ -17,7 +17,7 @@ exports.LazySet = function (vals) {
 
         Once somebody does an operation
         where sets are useful, such
-        as has/add/del, we convert it over
+        as has/add/delete, we convert it over
         to a set for a one-time cost.
     */
     const self = {};
@@ -63,10 +63,10 @@ exports.LazySet = function (vals) {
         self.set.add(val);
     };
 
-    self.del = function (v) {
+    self.delete = function (v) {
         make_set();
         const val = self._clean(v);
-        self.set.delete(val);
+        return self.set.delete(val);
     };
 
     self._clean = function (v) {
diff --git a/static/js/muting.js b/static/js/muting.js
index 87e49d448b..8f2fe9bb09 100644
--- a/static/js/muting.js
+++ b/static/js/muting.js
@@ -15,7 +15,7 @@ exports.add_muted_topic = function (stream_id, topic) {
 exports.remove_muted_topic = function (stream_id, topic) {
     const sub_dict = muted_topics.get(stream_id);
     if (sub_dict) {
-        sub_dict.del(topic);
+        sub_dict.delete(topic);
     }
 };
 
diff --git a/static/js/narrow_state.js b/static/js/narrow_state.js
index 0c60245d01..927ef68392 100644
--- a/static/js/narrow_state.js
+++ b/static/js/narrow_state.js
@@ -52,7 +52,7 @@ function collect_single(operators) {
     _.each(operators, function (elem) {
         const key = elem.operator;
         if (seen.has(key)) {
-            result.del(key);
+            result.delete(key);
         } else {
             result.set(key, elem.operand);
             seen.set(key, true);
diff --git a/static/js/people.js b/static/js/people.js
index 446caa1924..507d816b8e 100644
--- a/static/js/people.js
+++ b/static/js/people.js
@@ -984,7 +984,7 @@ exports.deactivate = function (person) {
     // We don't fully remove a person from all of our data
     // structures, because deactivated users can be part
     // of somebody's PM list.
-    active_user_dict.del(person.user_id);
+    active_user_dict.delete(person.user_id);
 };
 
 exports.report_late_add = function (user_id, email) {
@@ -1104,7 +1104,7 @@ exports.maybe_incr_recipient_count = function (message) {
 
 exports.set_full_name = function (person_obj, new_full_name) {
     if (people_by_name_dict.has(person_obj.full_name)) {
-        people_by_name_dict.del(person_obj.full_name);
+        people_by_name_dict.delete(person_obj.full_name);
     }
     // Remove previous and add new full name to the duplicate full name tracker.
     exports.track_duplicate_full_name(person_obj.full_name, person_obj.user_id, true);
diff --git a/static/js/stream_data.js b/static/js/stream_data.js
index acfd23ed4e..ca5026e6ef 100644
--- a/static/js/stream_data.js
+++ b/static/js/stream_data.js
@@ -60,18 +60,18 @@ const BinaryDict = function (pred) {
     };
 
     self.set_true = function (k, v) {
-        self.falses.del(k);
+        self.falses.delete(k);
         self.trues.set(k, v);
     };
 
     self.set_false = function (k, v) {
-        self.trues.del(k);
+        self.trues.delete(k);
         self.falses.set(k, v);
     };
 
-    self.del = function (k) {
-        self.trues.del(k);
-        self.falses.del(k);
+    self.delete = function (k) {
+        self.trues.delete(k);
+        self.falses.delete(k);
     };
 
 
@@ -133,7 +133,7 @@ exports.rename_sub = function (sub, new_name) {
     stream_ids_by_name.set(old_name, sub.stream_id);
 
     sub.name = new_name;
-    stream_info.del(old_name);
+    stream_info.delete(old_name);
     stream_info.set(new_name, sub);
 };
 
@@ -264,8 +264,8 @@ exports.delete_sub = function (stream_id) {
         blueslip.warn('Failed to delete stream ' + stream_id);
         return;
     }
-    subs_by_stream_id.del(stream_id);
-    stream_info.del(sub.name);
+    subs_by_stream_id.delete(stream_id);
+    stream_info.delete(sub.name);
 };
 
 exports.get_non_default_stream_names = function () {
@@ -633,7 +633,7 @@ exports.remove_subscriber = function (stream_name, user_id) {
         return false;
     }
 
-    sub.subscribers.del(user_id);
+    sub.subscribers.delete(user_id);
 
     return true;
 };
diff --git a/static/js/stream_list.js b/static/js/stream_list.js
index f1f5317c2c..8ff533001c 100644
--- a/static/js/stream_list.js
+++ b/static/js/stream_list.js
@@ -50,7 +50,7 @@ exports.stream_sidebar = (function () {
         // cases like removing the last pinned stream (and removing
         // the divider).
 
-        self.rows.del(stream_id);
+        self.rows.delete(stream_id);
     };
 
     return self;
diff --git a/static/js/topic_data.js b/static/js/topic_data.js
index 5200ff3ea2..4d9a5ae636 100644
--- a/static/js/topic_data.js
+++ b/static/js/topic_data.js
@@ -102,7 +102,7 @@ exports.topic_history = function (stream_id) {
         }
 
         if (existing.count <= 1) {
-            topics.del(topic_name);
+            topics.delete(topic_name);
             return;
         }
 
diff --git a/static/js/typeahead_helper.js b/static/js/typeahead_helper.js
index fd3a449cff..fb7206c162 100644
--- a/static/js/typeahead_helper.js
+++ b/static/js/typeahead_helper.js
@@ -91,7 +91,7 @@ exports.render_person = function (person) {
 };
 
 exports.clear_rendered_person = function (user_id) {
-    rendered.persons.del(user_id);
+    rendered.persons.delete(user_id);
 };
 
 exports.render_user_group = function (user_group) {
@@ -118,7 +118,7 @@ exports.render_person_or_user_group = function (item) {
 
 exports.clear_rendered_stream = function (stream_id) {
     if (rendered.streams.has(stream_id)) {
-        rendered.streams.del(stream_id);
+        rendered.streams.delete(stream_id);
     }
 };
 
diff --git a/static/js/unread.js b/static/js/unread.js
index 397d906be7..81cd02118e 100644
--- a/static/js/unread.js
+++ b/static/js/unread.js
@@ -48,7 +48,7 @@ function make_bucketer(options) {
         const bucket = reverse_lookup.get(item_id);
         if (bucket) {
             bucket.delete(item_id);
-            reverse_lookup.del(item_id);
+            reverse_lookup.delete(item_id);
         }
     };
 
@@ -112,7 +112,7 @@ exports.unread_pm_counter = (function () {
         }
     };
 
-    self.del = function (message_id) {
+    self.delete = function (message_id) {
         bucketer.delete(message_id);
     };
 
@@ -219,7 +219,7 @@ exports.unread_topic_counter = (function () {
         });
     };
 
-    self.del = function (msg_id) {
+    self.delete = function (msg_id) {
         bucketer.delete(msg_id);
     };
 
@@ -408,7 +408,7 @@ exports.update_unread_topics = function (msg, event) {
         return;
     }
 
-    exports.unread_topic_counter.del(
+    exports.unread_topic_counter.delete(
         msg.id
     );
 
@@ -452,8 +452,8 @@ exports.mark_as_read = function (message_id) {
     // We don't need to check anything about the message, since all
     // the following methods are cheap and work fine even if message_id
     // was never set to unread.
-    exports.unread_pm_counter.del(message_id);
-    exports.unread_topic_counter.del(message_id);
+    exports.unread_pm_counter.delete(message_id);
+    exports.unread_topic_counter.delete(message_id);
     exports.unread_mentions_counter.delete(message_id);
     unread_messages.delete(message_id);
 
diff --git a/static/js/user_groups.js b/static/js/user_groups.js
index 5037703247..6650e4c5d1 100644
--- a/static/js/user_groups.js
+++ b/static/js/user_groups.js
@@ -22,8 +22,8 @@ exports.add = function (user_group) {
 };
 
 exports.remove = function (user_group) {
-    user_group_name_dict.del(user_group.name);
-    user_group_by_id_dict.del(user_group.id);
+    user_group_name_dict.delete(user_group.name);
+    user_group_by_id_dict.delete(user_group.id);
 };
 
 exports.get_user_group_from_id = function (group_id, suppress_errors) {
@@ -40,12 +40,12 @@ exports.update = function (event) {
     const group = exports.get_user_group_from_id(event.group_id);
     if (event.data.name !== undefined) {
         group.name = event.data.name;
-        user_group_name_dict.del(group.name);
+        user_group_name_dict.delete(group.name);
         user_group_name_dict.set(group.name, group);
     }
     if (event.data.description !== undefined) {
         group.description = event.data.description;
-        user_group_name_dict.del(group.name);
+        user_group_name_dict.delete(group.name);
         user_group_name_dict.set(group.name, group);
     }
 };
diff --git a/static/js/user_status.js b/static/js/user_status.js
index 014c9f39d7..d439dc3638 100644
--- a/static/js/user_status.js
+++ b/static/js/user_status.js
@@ -51,7 +51,7 @@ exports.get_status_text = function (user_id) {
 
 exports.set_status_text = function (opts) {
     if (!opts.status_text) {
-        user_info.del(opts.user_id);
+        user_info.delete(opts.user_id);
         return;
     }