diff --git a/gulpfile.js b/gulpfile.js
index 8dc3cf57..5b7b50f0 100644
--- a/gulpfile.js
+++ b/gulpfile.js
@@ -126,8 +126,8 @@ const build = {
             gulp.task(name, () =>
                 gulp
                     .src(bundles[bundle].js[key])
-                    .pipe(concat(key))
                     .pipe(sourcemaps.init())
+                    .pipe(concat(key))
                     .pipe(
                         rollup(
                             {
diff --git a/package.json b/package.json
index 6dffeeef..67ccfe98 100644
--- a/package.json
+++ b/package.json
@@ -39,12 +39,12 @@
         "run-sequence": "^2.2.1",
         "stylelint": "^8.4.0",
         "stylelint-config-prettier": "^2.0.0",
-        "stylelint-config-sass-guidelines": "^4.0.1",
+        "stylelint-config-sass-guidelines": "^4.1.0",
         "stylelint-config-standard": "^18.0.0",
         "stylelint-order": "^0.8.0",
         "stylelint-scss": "^2.2.0",
         "stylelint-selector-bem-pattern": "^2.0.0",
-        "uglify-es": "^3.3.5"
+        "uglify-es": "^3.3.7"
     },
     "keywords": ["HTML5 Video", "HTML5 Audio", "Media Player", "DASH", "Shaka", "WordPress", "HLS"],
     "repository": {
diff --git a/src/js/controls.js b/src/js/controls.js
index 936bee6b..ea30acec 100644
--- a/src/js/controls.js
+++ b/src/js/controls.js
@@ -845,11 +845,11 @@ const controls = {
                 container.style.height = '';
 
                 // Only listen once
-                utils.off(container, utils.transitionEnd, restore);
+                utils.off(container, utils.transitionEndEvent, restore);
             };
 
             // Listen for the transition finishing and restore auto height/width
-            utils.on(container, utils.transitionEnd, restore);
+            utils.on(container, utils.transitionEndEvent, restore);
 
             // Set dimensions to target
             container.style.width = `${size.width}px`;
diff --git a/src/js/support.js b/src/js/support.js
index f75517d6..23a8ebef 100644
--- a/src/js/support.js
+++ b/src/js/support.js
@@ -151,7 +151,7 @@ const support = {
     touch: 'ontouchstart' in document.documentElement,
 
     // Detect transitions support
-    transitions: utils.transitionEnd !== false,
+    transitions: utils.transitionEndEvent !== false,
 
     // Reduced motion iOS & MacOS setting
     // https://webkit.org/blog/7551/responsive-design-for-motion/
diff --git a/src/js/utils.js b/src/js/utils.js
index 1b64fc8d..79ed5861 100644
--- a/src/js/utils.js
+++ b/src/js/utils.js
@@ -731,7 +731,7 @@ const utils = {
     },
 
     // Get the transition end event
-    transitionEnd: (() => {
+    get transitionEndEvent() {
         const element = document.createElement('span');
 
         const events = {
@@ -743,8 +743,8 @@ const utils = {
 
         const type = Object.keys(events).find(event => element.style[event] !== undefined);
 
-        return typeof type === 'string' ? type : false;
-    })(),
+        return utils.is.string(type) ? events[type] : false;
+    },
 
     // Force repaint of element
     repaint(element) {