diff --git a/src/extension.js b/src/extension.js
index d5c66cf..609673d 100644
--- a/src/extension.js
+++ b/src/extension.js
@@ -139,7 +139,7 @@ const WeatherMenuButton = new Lang.Class({
             text: _('...')
         });
 
-        if (typeof St.TextDirection == 'undefined') {
+        if (St.TextDirection == undefined) {
             // Panel icon
             this._weatherIcon = new St.Icon({
                 icon_name: 'view-refresh' + this.icon_type(),
@@ -191,7 +191,7 @@ const WeatherMenuButton = new Lang.Class({
                 Main.panel._rightBox.insert_child_at_index(this.actor, 0);
                 break;
         }
-        if (typeof Main.panel._menus == 'undefined')
+        if (Main.panel._menus == undefined)
             Main.panel.menuManager.addMenu(this.menu);
         else
             Main.panel._menus.addMenu(this.menu);
@@ -285,8 +285,8 @@ const WeatherMenuButton = new Lang.Class({
         this._settingsC = this._settings.connect("changed", function() {
             that.rebuildFutureWeatherUi();
             if (that.locationChanged()) {
-                that.currentWeatherCache = 'undefined';
-                that.forecastWeatherCache = 'undefined';
+                that.currentWeatherCache = undefined;
+                that.forecastWeatherCache = undefined;
             }
             that.parseWeatherCurrent();
             that.parseWeatherForecast();
@@ -303,8 +303,8 @@ const WeatherMenuButton = new Lang.Class({
         });
         this._settingsInterfaceC = this._settingsInterface.connect("changed", function() {
             if (that.locationChanged()) {
-                that.currentWeatherCache = 'undefined';
-                that.forecastWeatherCache = 'undefined';
+                that.currentWeatherCache = undefined;
+                that.forecastWeatherCache = undefined;
             }
             that.parseWeatherCurrent();
             that.parseWeatherForecast();
@@ -700,7 +700,7 @@ const WeatherMenuButton = new Lang.Class({
     },
 
     _onOpenStateChanged: function(menu, open) {
-        if (open && typeof this._forecastScrollBox != 'undefined' && typeof this._forecastBox != 'undefined' && typeof this._currentWeather != 'undefined') {
+        if (open && this._forecastScrollBox != undefined && this._forecastBox != undefined && this._currentWeather != undefined) {
             this._forecastScrollBox.set_width(this._currentWeather.get_width());
             if (this._forecastBox.get_width() > this._currentWeather.get_width()) {
                 this._forecastScrollBox.hscroll.margin_top = 10;
@@ -1094,7 +1094,7 @@ weather-storm.png = weather-storm-symbolic.svg
     },
 
     parseWeatherCurrent: function() {
-        if (this.currentWeatherCache == 'undefined') {
+        if (this.currentWeatherCache == undefined) {
             this.refreshWeatherCurrent();
             return;
         }
@@ -1154,10 +1154,10 @@ weather-storm.png = weather-storm-symbolic.svg
 
         let iconname = this.get_weather_icon_safely(json.weather[0].id, now < sunrise || now > sunset);
 
-        if (typeof this.lastBuildId == 'undefined')
+        if (this.lastBuildId == undefined)
             this.lastBuildId = 0;
 
-        if (typeof this.lastBuildDate == 'undefined')
+        if (this.lastBuildDate == undefined)
             this.lastBuildDate = 0;
 
         if (this.lastBuildId != json.dt || !this.lastBuildDate) {
@@ -1369,7 +1369,7 @@ weather-storm.png = weather-storm-symbolic.svg
     },
 
     parseWeatherForecast: function() {
-        if (this.forecastWeatherCache == 'undefined') {
+        if (this.forecastWeatherCache == undefined) {
             this.refreshWeatherForecast();
             return;
         }
@@ -1381,7 +1381,7 @@ weather-storm.png = weather-storm-symbolic.svg
         for (let i = 0; i < this._days_forecast; i++) {
             let forecastUi = this._forecast[i];
             let forecastData = forecast[i];
-            if (forecastData == 'undefined')
+            if (forecastData == undefined)
                 continue;
 
             let t_low = forecastData.temp.min;
diff --git a/src/prefs.js b/src/prefs.js
index db2fc17..19f6dc0 100644
--- a/src/prefs.js
+++ b/src/prefs.js
@@ -157,7 +157,7 @@ const WeatherPrefsWidget = new GObject.Class({
         this.Window.get_object("tree-toolbutton-remove").sensitive = Boolean(this.city.length);
 
         if (mCities != this.city) {
-            if (typeof this.liststore != "undefined")
+            if (this.liststore != undefined)
                 this.liststore.clear();
 
             if (this.city.length > 0) {
@@ -290,7 +290,7 @@ const WeatherPrefsWidget = new GObject.Class({
     selectionChanged: function(select) {
         let a = select.get_selected_rows(this.liststore)[0][0];
 
-        if (typeof a != "undefined")
+        if (a != undefined)
             if (this.actual_city != parseInt(a.to_string()))
                 this.actual_city = parseInt(a.to_string());
     },
@@ -350,7 +350,7 @@ const WeatherPrefsWidget = new GObject.Class({
                 id: id
             }, function() {
                 d.sensitive = 0;
-                if (typeof arguments[0] == "undefined")
+                if (arguments[0] == undefined)
                     return 0;
 
                 let city = arguments[0];
@@ -397,7 +397,7 @@ const WeatherPrefsWidget = new GObject.Class({
                     let current = this.liststore.get_iter_first();
 
                     for (var i in city) {
-                        if (typeof m == "undefined")
+                        if (m == undefined)
                             var m = {};
 
                         current = completionModel.append();
@@ -546,10 +546,10 @@ const WeatherPrefsWidget = new GObject.Class({
 
         let message = Soup.form_request_new_from_hash('GET', url, params);
 
-        if (typeof this.asyncSession == "undefined")
+        if (this.asyncSession == undefined)
             this.asyncSession = {};
 
-        if (typeof this.asyncSession[id] != "undefined" && this.asyncSession[id]) {
+        if (this.asyncSession[id] != undefined && this.asyncSession[id]) {
             _httpSession.abort();
             this.asyncSession[id] = 0;
         }