diff --git a/src/static/skins/colibris/index.js b/src/static/skins/colibris/index.js
index c56ba5bb6..633db7267 100644
--- a/src/static/skins/colibris/index.js
+++ b/src/static/skins/colibris/index.js
@@ -1,5 +1,7 @@
-function customStart() {
+'use strict';
+
+window.customStart = () => {
   // define your javascript here
   // jquery is available - except index.js
   // you can load extra scripts with $.getScript http://api.jquery.com/jQuery.getScript/
-}
+};
diff --git a/src/static/skins/colibris/pad.js b/src/static/skins/colibris/pad.js
index 0f5e47312..1987f3204 100644
--- a/src/static/skins/colibris/pad.js
+++ b/src/static/skins/colibris/pad.js
@@ -1,5 +1,7 @@
-function customStart() {
+'use strict';
+
+window.customStart = () => {
   $('#pad_title').show();
   $('.buttonicon').mousedown(function () { $(this).parent().addClass('pressed'); });
   $('.buttonicon').mouseup(function () { $(this).parent().removeClass('pressed'); });
-}
+};
diff --git a/src/static/skins/colibris/timeslider.js b/src/static/skins/colibris/timeslider.js
index 741011279..5fa8ae3b2 100644
--- a/src/static/skins/colibris/timeslider.js
+++ b/src/static/skins/colibris/timeslider.js
@@ -1,2 +1,4 @@
-function customStart() {
-}
+'use strict';
+
+window.customStart = () => {
+};
diff --git a/src/static/skins/no-skin/index.js b/src/static/skins/no-skin/index.js
index c56ba5bb6..633db7267 100644
--- a/src/static/skins/no-skin/index.js
+++ b/src/static/skins/no-skin/index.js
@@ -1,5 +1,7 @@
-function customStart() {
+'use strict';
+
+window.customStart = () => {
   // define your javascript here
   // jquery is available - except index.js
   // you can load extra scripts with $.getScript http://api.jquery.com/jQuery.getScript/
-}
+};
diff --git a/src/static/skins/no-skin/pad.js b/src/static/skins/no-skin/pad.js
index c56ba5bb6..633db7267 100644
--- a/src/static/skins/no-skin/pad.js
+++ b/src/static/skins/no-skin/pad.js
@@ -1,5 +1,7 @@
-function customStart() {
+'use strict';
+
+window.customStart = () => {
   // define your javascript here
   // jquery is available - except index.js
   // you can load extra scripts with $.getScript http://api.jquery.com/jQuery.getScript/
-}
+};
diff --git a/src/static/skins/no-skin/timeslider.js b/src/static/skins/no-skin/timeslider.js
index c56ba5bb6..633db7267 100644
--- a/src/static/skins/no-skin/timeslider.js
+++ b/src/static/skins/no-skin/timeslider.js
@@ -1,5 +1,7 @@
-function customStart() {
+'use strict';
+
+window.customStart = () => {
   // define your javascript here
   // jquery is available - except index.js
   // you can load extra scripts with $.getScript http://api.jquery.com/jQuery.getScript/
-}
+};