diff --git a/html/src/app.js b/html/src/app.js
index 18f2a185..6ae29dfc 100644
--- a/html/src/app.js
+++ b/html/src/app.js
@@ -294,7 +294,7 @@ speechSynthesis.getVoices();
     API.$emit = function (name, ...args) {
         // console.log(name, ...args);
         var handlers = this.eventHandlers.get(name);
-        if (handlers === undefined) {
+        if (typeof handlers === 'undefined') {
             return;
         }
         try {
@@ -308,7 +308,7 @@ speechSynthesis.getVoices();
 
     API.$on = function (name, handler) {
         var handlers = this.eventHandlers.get(name);
-        if (handlers === undefined) {
+        if (typeof handlers === 'undefined') {
             handlers = [];
             this.eventHandlers.set(name, handlers);
         }
@@ -317,7 +317,7 @@ speechSynthesis.getVoices();
 
     API.$off = function (name, handler) {
         var handlers = this.eventHandlers.get(name);
-        if (handlers === undefined) {
+        if (typeof handlers === 'undefined') {
             return;
         }
         var { length } = handlers;
@@ -354,7 +354,7 @@ speechSynthesis.getVoices();
             }
             // merge requests
             var req = this.pendingGetRequests.get(init.url);
-            if (req !== undefined) {
+            if (typeof req !== 'undefined') {
                 return req;
             }
         } else if (init.VRCPlusIcon) {
@@ -502,16 +502,16 @@ speechSynthesis.getVoices();
         var text = [];
         if (code > 0) {
             var status = this.statusCodes[code];
-            if (status === undefined) {
+            if (typeof status === 'undefined') {
                 text.push(`${code}`);
             } else {
                 text.push(`${code} ${status}`);
             }
         }
-        if (error !== undefined) {
+        if (typeof error !== 'undefined') {
             text.push(JSON.stringify(error));
         }
-        if (extra !== undefined) {
+        if (typeof extra !== 'undefined') {
             text.push(JSON.stringify(extra));
         }
         text = text.map((s) => escapeTag(s)).join('<br>');
@@ -525,7 +525,7 @@ speechSynthesis.getVoices();
     };
 
     API.$bulk = function (options, args) {
-        if (options.handle !== undefined) {
+        if ('handle' in options) {
             options.handle.call(this, args, options);
         }
         if (args.json.length > 0 &&
@@ -537,7 +537,7 @@ speechSynthesis.getVoices();
                         ? args.json.length
                         : options.params.n === args.json.length)) {
             this.bulk(options);
-        } else if (options.done !== undefined) {
+        } else if ('done' in options) {
             options.done.call(this, true, options);
         }
         return args;
@@ -545,7 +545,7 @@ speechSynthesis.getVoices();
 
     API.bulk = function (options) {
         this[options.fn](options.params).catch((err) => {
-            if (options.done !== undefined) {
+            if ('done' in options) {
                 options.done.call(this, false, options);
             }
             throw err;
@@ -766,7 +766,7 @@ speechSynthesis.getVoices();
                     this.text = 'Private';
                 } else if (L.worldId) {
                     var ref = API.cachedWorlds.get(L.worldId);
-                    if (ref === undefined) {
+                    if (typeof ref === 'undefined') {
                         API.getWorld({
                             worldId: L.worldId
                         }).then((args) => {
@@ -1037,7 +1037,7 @@ speechSynthesis.getVoices();
             }
             var key = tag.substr(9);
             var value = subsetOfLanguages[key];
-            if (value === undefined) {
+            if (typeof value === 'undefined') {
                 continue;
             }
             ref.$languages.push({
@@ -1157,7 +1157,7 @@ speechSynthesis.getVoices();
             json.$online_for = API.currentUser.$online_for;
             json.$offline_for = API.currentUser.$offline_for;
         }
-        if (ref === undefined) {
+        if (typeof ref === 'undefined') {
             ref = {
                 id: '',
                 username: '',
@@ -1276,7 +1276,7 @@ speechSynthesis.getVoices();
     API.getCachedUser = function (params) {
         return new Promise((resolve, reject) => {
             var ref = this.cachedUsers.get(params.userId);
-            if (ref === undefined) {
+            if (typeof ref === 'undefined') {
                 this.getUser(params).catch(reject).then(resolve);
             } else {
                 resolve({
@@ -1391,7 +1391,7 @@ speechSynthesis.getVoices();
 
     API.applyWorld = function (json) {
         var ref = this.cachedWorlds.get(json.id);
-        if (ref === undefined) {
+        if (typeof ref === 'undefined') {
             ref = {
                 id: '',
                 name: '',
@@ -1462,7 +1462,7 @@ speechSynthesis.getVoices();
     API.getCachedWorld = function (params) {
         return new Promise((resolve, reject) => {
             var ref = this.cachedWorlds.get(params.worldId);
-            if (ref === undefined) {
+            if (typeof ref === 'undefined') {
                 this.getWorld(params).catch(reject).then(resolve);
             } else {
                 resolve({
@@ -1491,7 +1491,7 @@ speechSynthesis.getVoices();
     */
     API.getWorlds = function (params, option) {
         var endpoint = 'worlds';
-        if (option !== undefined) {
+        if (typeof option !== 'undefined') {
             endpoint = `worlds/${option}`;
         }
         return this.call(endpoint, {
@@ -1724,7 +1724,7 @@ speechSynthesis.getVoices();
 
     API.applyAvatar = function (json) {
         var ref = this.cachedAvatars.get(json.id);
-        if (ref === undefined) {
+        if (typeof ref === 'undefined') {
             ref = {
                 id: '',
                 name: '',
@@ -1778,7 +1778,7 @@ speechSynthesis.getVoices();
     API.getCachedAvatar = function (params) {
         return new Promise((resolve, reject) => {
             var ref = this.cachedAvatars.get(params.avatarId);
-            if (ref === undefined) {
+            if (typeof ref === 'undefined') {
                 this.getAvatar(params).catch(reject).then(resolve);
             } else {
                 resolve({
@@ -1884,7 +1884,7 @@ speechSynthesis.getVoices();
 
     API.$on('NOTIFICATION:ACCEPT', function (args) {
         var ref = this.cachedNotifications.get(args.params.notificationId);
-        if (ref === undefined ||
+        if (typeof ref === 'undefined' ||
             ref.$isDeleted) {
             return;
         }
@@ -1905,7 +1905,7 @@ speechSynthesis.getVoices();
 
     API.$on('NOTIFICATION:HIDE', function (args) {
         var ref = this.cachedNotifications.get(args.params.notificationId);
-        if (ref === undefined &&
+        if (typeof ref === 'undefined' &&
             ref.$isDeleted) {
             return;
         }
@@ -1921,7 +1921,7 @@ speechSynthesis.getVoices();
 
     API.applyNotification = function (json) {
         var ref = this.cachedNotifications.get(json.id);
-        if (ref === undefined) {
+        if (typeof ref === 'undefined') {
             ref = {
                 id: '',
                 senderUserId: '',
@@ -2180,7 +2180,7 @@ speechSynthesis.getVoices();
 
     API.applyPlayerModeration = function (json) {
         var ref = this.cachedPlayerModerations.get(json.id);
-        if (ref === undefined) {
+        if (typeof ref === 'undefined') {
             ref = {
                 id: '',
                 type: '',
@@ -2374,7 +2374,7 @@ speechSynthesis.getVoices();
 
     API.$on('FAVORITE:DELETE', function (args) {
         var ref = this.cachedFavoritesByObjectId.get(args.params.objectId);
-        if (ref === undefined) {
+        if (typeof ref === 'undefined') {
             return;
         }
         // 애초에 $isDeleted인데 여기로 올 수 가 있나..?
@@ -2486,7 +2486,7 @@ speechSynthesis.getVoices();
 
     API.applyFavorite = function (json) {
         var ref = this.cachedFavorites.get(json.id);
-        if (ref === undefined) {
+        if (typeof ref === 'undefined') {
             ref = {
                 id: '',
                 type: '',
@@ -2510,7 +2510,7 @@ speechSynthesis.getVoices();
         if (ref.$isDeleted === false &&
             ref.$groupRef === null) {
             var group = this.cachedFavoriteGroupsByTypeName.get(ref.$groupKey);
-            if (group !== undefined) {
+            if (typeof group !== 'undefined') {
                 ref.$groupRef = group;
                 ++group.count;
             }
@@ -2552,7 +2552,7 @@ speechSynthesis.getVoices();
                 continue;
             }
             var type = types[ref.type];
-            if (type === undefined) {
+            if (typeof type === 'undefined') {
                 continue;
             }
             if ((ref.type === 'avatar') && (!tags.includes(ref.tags[0]))) {
@@ -2615,7 +2615,7 @@ speechSynthesis.getVoices();
 
     API.applyFavoriteGroup = function (json) {
         var ref = this.cachedFavoriteGroups.get(json.id);
-        if (ref === undefined) {
+        if (typeof ref === 'undefined') {
             ref = {
                 id: '',
                 ownerId: '',
@@ -2702,7 +2702,7 @@ speechSynthesis.getVoices();
                 continue;
             }
             var groups = types[ref.type];
-            if (groups === undefined) {
+            if (typeof groups === 'undefined') {
                 continue;
             }
             for (var group of groups) {
@@ -2730,7 +2730,7 @@ speechSynthesis.getVoices();
                 continue;
             }
             var groups = types[ref.type];
-            if (groups === undefined) {
+            if (typeof groups === 'undefined') {
                 continue;
             }
             for (var group of groups) {
@@ -2760,7 +2760,7 @@ speechSynthesis.getVoices();
                 continue;
             }
             var group = this.cachedFavoriteGroupsByTypeName.get(ref.$groupKey);
-            if (group === undefined) {
+            if (typeof group === 'undefined') {
                 continue;
             }
             ref.$groupRef = group;
@@ -3400,7 +3400,7 @@ speechSynthesis.getVoices();
     $app.methods.languageClass = function (language) {
         var style = {};
         var mapping = languageMappings[language];
-        if (mapping !== undefined) {
+        if (typeof mapping !== 'undefined') {
             style[mapping] = true;
         }
         return style;
@@ -3670,8 +3670,8 @@ speechSynthesis.getVoices();
         };
         for (var userId of friends) {
             var ref = this.friends.get(userId);
-            var name = (ref !== undefined && ref.name) || '';
-            var memo = (ref !== undefined && ref.memo) || '';
+            var name = (typeof ref !== 'undefined' && ref.name) || '';
+            var memo = (typeof ref !== 'undefined' && ref.memo) || '';
             lines.push(`${_(userId)},${_(name)},${_(memo)}`);
         }
         this.exportFriendsListContent = lines.join('\n');
@@ -3715,7 +3715,7 @@ speechSynthesis.getVoices();
             var credentialsToSave = { user: currentUser, loginParmas: this.saveCredentials };
             savedCredentialsArray[currentUser.username] = credentialsToSave;
             delete this.saveCredentials;
-        } else if (savedCredentialsArray[currentUser.username] !== undefined) {
+        } else if (typeof savedCredentialsArray[currentUser.username] !== 'undefined') {
             savedCredentialsArray[currentUser.username].user = currentUser;
         }
         this.loginForm.savedCredentials = savedCredentialsArray;
@@ -3757,7 +3757,7 @@ speechSynthesis.getVoices();
 
     API.$on('AUTOLOGIN', function () {
         var user = $app.loginForm.savedCredentials[$app.loginForm.lastUserLoggedIn];
-        if (user !== undefined) {
+        if (typeof user !== 'undefined') {
             $app.relogin({
                 username: user.loginParmas.username,
                 password: user.loginParmas.password
@@ -3924,7 +3924,7 @@ speechSynthesis.getVoices();
                 continue;
             }
             var user = API.cachedUsers.get(userId);
-            if (user !== undefined &&
+            if (typeof user !== 'undefined' &&
                 user.status !== 'offline') {
                 continue;
             }
@@ -4034,9 +4034,9 @@ speechSynthesis.getVoices();
             no: ++this.friendsNo,
             memo: this.loadMemo(id)
         };
-        if (ref === undefined) {
+        if (typeof ref === 'undefined') {
             ref = this.friendLog[id];
-            if (ref !== undefined &&
+            if (typeof ref !== 'undefined' &&
                 ref.displayName) {
                 ctx.name = ref.displayName;
             }
@@ -4067,7 +4067,7 @@ speechSynthesis.getVoices();
 
     $app.methods.deleteFriend = function (id) {
         var ctx = this.friends.get(id);
-        if (ctx === undefined) {
+        if (typeof ctx === 'undefined') {
             return;
         }
         this.friends.delete(id);
@@ -4090,12 +4090,12 @@ speechSynthesis.getVoices();
 
     $app.methods.updateFriend = function (id, state, origin) {
         var ctx = this.friends.get(id);
-        if (ctx === undefined) {
+        if (typeof ctx === 'undefined') {
             return;
         }
         var ref = API.cachedUsers.get(id);
         var isVIP = API.cachedFavoritesByObjectId.has(id);
-        if (state === undefined ||
+        if (typeof state === 'undefined' ||
             ctx.state === state) {
             // this is should be: undefined -> user
             if (ctx.ref !== ref) {
@@ -4137,7 +4137,7 @@ speechSynthesis.getVoices();
                     }
                 }
             }
-            if (ref !== undefined &&
+            if (typeof ref !== 'undefined' &&
                 ctx.name !== ref.displayName) {
                 ctx.name = ref.displayName;
                 if (ctx.state === 'online') {
@@ -4155,7 +4155,7 @@ speechSynthesis.getVoices();
             // FIXME: 도배 가능성 있음
             if (origin &&
                 ctx.state !== 'online' &&
-                ref !== undefined &&
+                typeof ref !== 'undefined' &&
                 ref.location !== '' &&
                 ref.location !== 'offline') {
                 API.getUser({
@@ -4186,7 +4186,7 @@ speechSynthesis.getVoices();
             if (ctx.isVIP !== isVIP) {
                 ctx.isVIP = isVIP;
             }
-            if (ref !== undefined) {
+            if (typeof ref !== 'undefined') {
                 if (ctx.ref !== ref) {
                     ctx.ref = ref;
                 }
@@ -4213,7 +4213,7 @@ speechSynthesis.getVoices();
                 this.friendsGroup3_.push(ctx);
                 this.friendsGroupD_.unshift(ctx);
             }
-            if (ctx.ref !== undefined) {
+            if ('ref' in ctx) {
                 if ((ctx.ref.$offline_for === '') &&
                     ((ctx.state === 'offline') && ctx.ref.state === '') ||
                     (((ctx.state === 'offline') || (ctx.state === 'active')) &&
@@ -4319,7 +4319,7 @@ speechSynthesis.getVoices();
 
     $app.methods.userStatusClass = function (user) {
         var style = {};
-        if (user !== undefined) {
+        if (typeof user !== 'undefined') {
             if (user.location === 'offline') {
                 // Offline
                 style.offline = true;
@@ -4365,7 +4365,7 @@ speechSynthesis.getVoices();
         if (query) {
             var QUERY = query.toUpperCase();
             for (var ctx of this.friends.values()) {
-                if (ctx.ref === undefined) {
+                if (('ref' in ctx) === false) {
                     continue;
                 }
                 var NAME = ctx.name.toUpperCase();
@@ -4780,7 +4780,7 @@ speechSynthesis.getVoices();
 
     $app.methods.updateDiscord = function () {
         var ref = API.cachedUsers.get(API.currentUser.id);
-        if (ref !== undefined) {
+        if (typeof ref !== 'undefined') {
             var myLocation = (this.isGameRunning === true)
                 ? this.lastLocation
                 : '';
@@ -4912,7 +4912,7 @@ speechSynthesis.getVoices();
             var map = new Map();
             for (var json of args.json) {
                 var ref = API.cachedUsers.get(json.id);
-                if (ref !== undefined) {
+                if (typeof ref !== 'undefined') {
                     map.set(ref.id, ref);
                 }
             }
@@ -4997,7 +4997,7 @@ speechSynthesis.getVoices();
             var map = new Map();
             for (var json of args.json) {
                 var ref = API.cachedWorlds.get(json.id);
-                if (ref !== undefined) {
+                if (typeof ref !== 'undefined') {
                     map.set(ref.id, ref);
                 }
             }
@@ -5048,7 +5048,7 @@ speechSynthesis.getVoices();
             var map = new Map();
             for (var json of args.json) {
                 var ref = API.cachedAvatars.get(json.id);
-                if (ref !== undefined) {
+                if (typeof ref !== 'undefined') {
                     map.set(ref.id, ref);
                 }
             }
@@ -5100,9 +5100,9 @@ speechSynthesis.getVoices();
     $app.methods.applyFavorite = function (type, objectId) {
         var favorite = API.cachedFavoritesByObjectId.get(objectId);
         var ctx = this.favoriteObjects.get(objectId);
-        if (favorite !== undefined) {
+        if (typeof favorite !== 'undefined') {
             var isTypeChanged = false;
-            if (ctx === undefined) {
+            if (typeof ctx === 'undefined') {
                 ctx = {
                     id: objectId,
                     type,
@@ -5113,9 +5113,9 @@ speechSynthesis.getVoices();
                 this.favoriteObjects.set(objectId, ctx);
                 if (type === 'friend') {
                     var ref = API.cachedUsers.get(objectId);
-                    if (ref === undefined) {
+                    if (typeof ref === 'undefined') {
                         ref = this.friendLog[objectId];
-                        if (ref !== undefined &&
+                        if (typeof ref !== 'undefined' &&
                             ref.displayName) {
                             ctx.name = ref.displayName;
                         }
@@ -5125,13 +5125,13 @@ speechSynthesis.getVoices();
                     }
                 } else if (type === 'world') {
                     var ref = API.cachedWorlds.get(objectId);
-                    if (ref !== undefined) {
+                    if (typeof ref !== 'undefined') {
                         ctx.ref = ref;
                         ctx.name = ref.name;
                     }
                 } else if (type === 'avatar') {
                     var ref = API.cachedAvatars.get(objectId);
-                    if (ref !== undefined) {
+                    if (typeof ref !== 'undefined') {
                         ctx.ref = ref;
                         ctx.name = ref.name;
                     }
@@ -5151,7 +5151,7 @@ speechSynthesis.getVoices();
                 }
                 if (type === 'friend') {
                     var ref = API.cachedUsers.get(objectId);
-                    if (ref !== undefined) {
+                    if (typeof ref !== 'undefined') {
                         if (ctx.ref !== ref) {
                             ctx.ref = ref;
                         }
@@ -5162,7 +5162,7 @@ speechSynthesis.getVoices();
                     }
                 } else if (type === 'world') {
                     var ref = API.cachedWorlds.get(objectId);
-                    if (ref !== undefined) {
+                    if (typeof ref !== 'undefined') {
                         if (ctx.ref !== ref) {
                             ctx.ref = ref;
                         }
@@ -5173,7 +5173,7 @@ speechSynthesis.getVoices();
                     }
                 } else if (type === 'avatar') {
                     var ref = API.cachedAvatars.get(objectId);
-                    if (ref !== undefined) {
+                    if (typeof ref !== 'undefined') {
                         if (ctx.ref !== ref) {
                             ctx.ref = ref;
                         }
@@ -5196,7 +5196,7 @@ speechSynthesis.getVoices();
                     this.sortFavoriteAvatars = true;
                 }
             }
-        } else if (ctx !== undefined) {
+        } else if (typeof ctx !== 'undefined') {
             this.favoriteObjects.delete(objectId);
             if (type === 'friend') {
                 removeFromArray(this.favoriteFriends_, ctx);
@@ -5348,7 +5348,7 @@ speechSynthesis.getVoices();
 
     API.$on('FRIEND:REQUEST', function (args) {
         var ref = this.cachedUsers.get(args.params.userId);
-        if (ref === undefined) {
+        if (typeof ref === 'undefined') {
             return;
         }
         $app.friendLogTable.data.push({
@@ -5362,7 +5362,7 @@ speechSynthesis.getVoices();
 
     API.$on('FRIEND:REQUEST:CANCEL', function (args) {
         var ref = this.cachedUsers.get(args.params.userId);
-        if (ref === undefined) {
+        if (typeof ref === 'undefined') {
             return;
         }
         $app.friendLogTable.data.push({
@@ -5400,7 +5400,7 @@ speechSynthesis.getVoices();
                     id
                 };
                 var user = API.cachedUsers.get(id);
-                if (user !== undefined) {
+                if (typeof user !== 'undefined') {
                     ctx.displayName = user.displayName;
                     ctx.trustLevel = user.$trustLevel;
                 }
@@ -5413,7 +5413,7 @@ speechSynthesis.getVoices();
     };
 
     $app.methods.addFriendship = function (id) {
-        if (this.friendLog[id] !== undefined) {
+        if (typeof this.friendLog[id] !== 'undefined') {
             return;
         }
         var ctx = {
@@ -5423,7 +5423,7 @@ speechSynthesis.getVoices();
         };
         Vue.set(this.friendLog, id, ctx);
         var ref = API.cachedUsers.get(id);
-        if (ref !== undefined) {
+        if (typeof ref !== 'undefined') {
             ctx.displayName = ref.displayName;
             ctx.trustLevel = ref.$trustLevel;
             this.friendLogTable.data.push({
@@ -5439,7 +5439,7 @@ speechSynthesis.getVoices();
 
     $app.methods.deleteFriendship = function (id) {
         var ctx = this.friendLog[id];
-        if (ctx === undefined) {
+        if (typeof ctx === 'undefined') {
             return;
         }
         Vue.delete(this.friendLog, id);
@@ -5468,7 +5468,7 @@ speechSynthesis.getVoices();
 
     $app.methods.updateFriendship = function (ref) {
         var ctx = this.friendLog[ref.id];
-        if (ctx === undefined) {
+        if (typeof ctx === 'undefined') {
             return;
         }
         if (ctx.displayName !== ref.displayName) {
@@ -6309,7 +6309,7 @@ speechSynthesis.getVoices();
         // 얘는 @DELETE가 오고나서 ACCEPT가 옴
         // 따라서 $isDeleted라면 ref가 undefined가 됨
         if (D.visible === false ||
-            ref === undefined ||
+            typeof ref === 'undefined' ||
             ref.type !== 'friendRequest' ||
             ref.senderUserId !== D.id) {
             return;
@@ -6466,7 +6466,7 @@ speechSynthesis.getVoices();
         D.$location = L;
         if (L.userId) {
             var ref = API.cachedUsers.get(L.userId);
-            if (ref === undefined) {
+            if (typeof ref === 'undefined') {
                 API.getUser({
                     userId: L.userId
                 }).then((args) => {
@@ -6480,7 +6480,7 @@ speechSynthesis.getVoices();
         var users = [];
         if (L.isOffline === false) {
             for (var { ref } of this.friends.values()) {
-                if (ref !== undefined &&
+                if (typeof ref !== 'undefined' &&
                     ref.location === L.tag) {
                     users.push(ref);
                 }
@@ -6489,7 +6489,7 @@ speechSynthesis.getVoices();
         if (this.isGameRunning &&
             this.lastLocation === L.tag) {
             var ref = API.cachedUsers.get(API.currentUser.id);
-            users.push((ref === undefined)
+            users.push((typeof ref === 'undefined')
                 ? API.currentUser
                 : ref);
         }
@@ -6509,7 +6509,7 @@ speechSynthesis.getVoices();
                 }
             };
             var ref = API.cachedWorlds.get(L.worldId);
-            if (ref === undefined) {
+            if (typeof ref === 'undefined') {
                 API.getWorld({
                     worldId: L.worldId
                 }).then((args) => {
@@ -6576,7 +6576,7 @@ speechSynthesis.getVoices();
             handle: (args) => {
                 for (var json of args.json) {
                     var $ref = API.cachedWorlds.get(json.id);
-                    if ($ref !== undefined) {
+                    if (typeof $ref !== 'undefined') {
                         map.set($ref.id, $ref);
                     }
                 }
@@ -6623,7 +6623,7 @@ speechSynthesis.getVoices();
             handle: (args) => {
                 for (var json of args.json) {
                     var $ref = API.cachedAvatars.get(json.id);
-                    if ($ref !== undefined) {
+                    if (typeof $ref !== 'undefined') {
                         map.set($ref.id, $ref);
                     }
                 }
@@ -6985,7 +6985,7 @@ speechSynthesis.getVoices();
         }
         var { instanceId } = D.$location;
         if (instanceId &&
-            instances[instanceId] === undefined) {
+            typeof instances[instanceId] === 'undefined') {
             instances[instanceId] = {
                 id: instanceId,
                 occupants: 0,
@@ -6993,14 +6993,14 @@ speechSynthesis.getVoices();
             };
         }
         for (var { ref } of this.friends.values()) {
-            if (ref === undefined ||
-                ref.$location === undefined ||
+            if (typeof ref === 'undefined' ||
+                ('$location' in ref) === false ||
                 ref.$location.worldId !== D.id) {
                 continue;
             }
             var { instanceId } = ref.$location;
             var instance = instances[instanceId];
-            if (instance === undefined) {
+            if (typeof instance === 'undefined') {
                 instance = {
                     id: instanceId,
                     occupants: 0,
@@ -7014,7 +7014,7 @@ speechSynthesis.getVoices();
             var lastLocation$ = API.parseLocation(this.lastLocation);
             if (lastLocation$.worldId === D.id) {
                 var instance = instances[lastLocation$.instanceId];
-                if (instance === undefined) {
+                if (typeof instance === 'undefined') {
                     instance = {
                         id: lastLocation$.instanceId,
                         occupants: 1,
@@ -7023,7 +7023,7 @@ speechSynthesis.getVoices();
                     instances[instance.id] = instance;
                 }
                 var ref = API.cachedUsers.get(API.currentUser.id);
-                instance.users.push((ref === undefined)
+                instance.users.push((typeof ref === 'undefined')
                     ? API.currentUser
                     : ref);
             }
@@ -7037,7 +7037,7 @@ speechSynthesis.getVoices();
             instance.$location = L;
             if (L.userId) {
                 var ref = API.cachedUsers.get(L.userId);
-                if (ref === undefined) {
+                if (typeof ref === 'undefined') {
                     API.getUser({
                         userId: L.userId
                     }).then((args) => {
diff --git a/html/src/vr.js b/html/src/vr.js
index db1d82b1..0a0e6695 100644
--- a/html/src/vr.js
+++ b/html/src/vr.js
@@ -115,7 +115,7 @@ speechSynthesis.getVoices();
     API.$emit = function (name, ...args) {
         // console.log(name, ...args);
         var handlers = this.eventHandlers.get(name);
-        if (handlers === undefined) {
+        if (typeof handlers === 'undefined') {
             return;
         }
         try {
@@ -129,7 +129,7 @@ speechSynthesis.getVoices();
 
     API.$on = function (name, handler) {
         var handlers = this.eventHandlers.get(name);
-        if (handlers === undefined) {
+        if (typeof handlers === 'undefined') {
             handlers = [];
             this.eventHandlers.set(name, handlers);
         }
@@ -138,7 +138,7 @@ speechSynthesis.getVoices();
 
     API.$off = function (name, handler) {
         var handlers = this.eventHandlers.get(name);
-        if (handlers === undefined) {
+        if (typeof handlers === 'undefined') {
             return;
         }
         var { length } = handlers;
@@ -176,7 +176,7 @@ speechSynthesis.getVoices();
             }
             // merge requests
             var req = this.pendingGetRequests.get(init.url);
-            if (req !== undefined) {
+            if (typeof req !== 'undefined') {
                 return req;
             }
         } else {
@@ -316,13 +316,13 @@ speechSynthesis.getVoices();
         var text = [];
         if (code > 0) {
             var status = this.statusCodes[code];
-            if (status === undefined) {
+            if (typeof status === 'undefined') {
                 text.push(`${code}`);
             } else {
                 text.push(`${code} ${status}`);
             }
         }
-        if (error !== undefined) {
+        if (typeof error !== 'undefined') {
             text.push(JSON.stringify(error));
         }
         text = text.map((s) => escapeTag(s)).join('<br>');
@@ -462,7 +462,7 @@ speechSynthesis.getVoices();
                     this.text = 'Private';
                 } else if (L.worldId) {
                     var ref = API.cachedWorlds.get(L.worldId);
-                    if (ref === undefined) {
+                    if (typeof ref === 'undefined') {
                         API.getWorld({
                             worldId: L.worldId
                         }).then((args) => {
@@ -503,7 +503,7 @@ speechSynthesis.getVoices();
 
     API.applyWorld = function (json) {
         var ref = this.cachedWorlds.get(json.id);
-        if (ref === undefined) {
+        if (typeof ref === 'undefined') {
             ref = {
                 id: '',
                 name: '',
@@ -577,7 +577,7 @@ speechSynthesis.getVoices();
 
     API.applyUser = function (json) {
         var ref = this.cachedUsers.get(json.id);
-        if (ref === undefined) {
+        if (typeof ref === 'undefined') {
             ref = {
                 id: '',
                 username: '',
@@ -659,7 +659,7 @@ speechSynthesis.getVoices();
     API.getCachedUser = function (params) {
         return new Promise((resolve, reject) => {
             var ref = this.cachedUsers.get(params.userId);
-            if (ref === undefined) {
+            if (typeof ref === 'undefined') {
                 this.getUser(params).catch(reject).then(resolve);
             } else {
                 resolve({
@@ -810,7 +810,7 @@ speechSynthesis.getVoices();
         if (feeds === null) {
             return;
         }
-        if ((this.lastFeedEntry !== undefined) &&
+        if (('lastFeedEntry' in this) &&
             (feeds[0].created_at === this.lastFeedEntry.created_at)) {
             return;
         }
@@ -1156,7 +1156,7 @@ speechSynthesis.getVoices();
 
     $app.methods.userStatusClass = function (user) {
         var style = {};
-        if (user !== undefined) {
+        if (typeof user !== 'undefined') {
             if (user.location === 'offline') {
                 // Offline
                 style.offline = true;
@@ -1186,7 +1186,7 @@ speechSynthesis.getVoices();
             text = 'Private';
         } else if (L.worldId) {
             var ref = API.cachedWorlds.get(L.worldId);
-            if (ref === undefined) {
+            if (typeof ref === 'undefined') {
                 await API.getWorld({
                     worldId: L.worldId
                 }).then((args) => {