From d974751ecbce91039bbca0784527cf03a5e75b70 Mon Sep 17 00:00:00 2001
From: mister-ben <git@misterben.me>
Date: Thu, 22 Jun 2017 07:10:09 +0100
Subject: [PATCH 1/3] Use passive event listenes for touchstart/touchmove

---
 src/js/utils/events.js | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/src/js/utils/events.js b/src/js/utils/events.js
index 97e4594fcc..664b35de72 100644
--- a/src/js/utils/events.js
+++ b/src/js/utils/events.js
@@ -202,6 +202,23 @@ export function fixEvent(event) {
   return event;
 }
 
+/**
+ * Whether passive event listeners are supported
+ */
+let _supportsPassive = false;
+
+try {
+  const opts = Object.defineProperty({}, 'passive', {
+    get() {
+      _supportsPassive = true;
+    }
+  });
+
+  window.addEventListener('test', null, opts);
+} catch (e) {
+  // disregard
+}
+
 /**
  * Add an event listener to element
  * It stores the handler function in a separate cache object
@@ -273,7 +290,13 @@ export function on(elem, type, fn) {
 
   if (data.handlers[type].length === 1) {
     if (elem.addEventListener) {
-      elem.addEventListener(type, data.dispatcher, false);
+      let options = false;
+
+      if (_supportsPassive &&
+        ['touchstart', 'touchmove'].indexOf(type) > -1) {
+        options = {passive: true};
+      }
+      elem.addEventListener(type, data.dispatcher, options);
     } else if (elem.attachEvent) {
       elem.attachEvent('on' + type, data.dispatcher);
     }

From a3a3d76f73489eb097df88d43f5f93e4fda156b4 Mon Sep 17 00:00:00 2001
From: mister-ben <git@misterben.me>
Date: Mon, 26 Jun 2017 11:11:47 +0100
Subject: [PATCH 2/3] Define passive events

---
 src/js/utils/events.js | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/src/js/utils/events.js b/src/js/utils/events.js
index 664b35de72..0a40dcb3aa 100644
--- a/src/js/utils/events.js
+++ b/src/js/utils/events.js
@@ -219,6 +219,14 @@ try {
   // disregard
 }
 
+/**
+ * Touch events Chrome expects to be passive
+ */
+const passiveEvents = [
+  'touchstart',
+  'touchmove'
+];
+
 /**
  * Add an event listener to element
  * It stores the handler function in a separate cache object
@@ -293,7 +301,7 @@ export function on(elem, type, fn) {
       let options = false;
 
       if (_supportsPassive &&
-        ['touchstart', 'touchmove'].indexOf(type) > -1) {
+        passiveEvents.indexOf(type) > -1) {
         options = {passive: true};
       }
       elem.addEventListener(type, data.dispatcher, options);

From f9888748a517699f905c4758456491293955325d Mon Sep 17 00:00:00 2001
From: mister-ben <git@misterben.me>
Date: Mon, 26 Jun 2017 11:53:14 +0100
Subject: [PATCH 3/3] Wrap try-catch in IIFE

---
 src/js/utils/events.js | 22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/src/js/utils/events.js b/src/js/utils/events.js
index 0a40dcb3aa..a98c39fb55 100644
--- a/src/js/utils/events.js
+++ b/src/js/utils/events.js
@@ -207,17 +207,19 @@ export function fixEvent(event) {
  */
 let _supportsPassive = false;
 
-try {
-  const opts = Object.defineProperty({}, 'passive', {
-    get() {
-      _supportsPassive = true;
-    }
-  });
+(function() {
+  try {
+    const opts = Object.defineProperty({}, 'passive', {
+      get() {
+        _supportsPassive = true;
+      }
+    });
 
-  window.addEventListener('test', null, opts);
-} catch (e) {
-  // disregard
-}
+    window.addEventListener('test', null, opts);
+  } catch (e) {
+    // disregard
+  }
+})();
 
 /**
  * Touch events Chrome expects to be passive