Change isTouchEnabledDevice to a function

So that the presence of `ontouchstart` method can be checked in the
runtime

js/src/carousel.js

@@ -12,6 +12,7 @@ import {
   getElementFromSelector,
   getTransitionDurationFromElement,
   isVisible,
+  isTouchEnabledDevice,
   reflow,
   triggerTransitionEnd,
   typeCheckConfig
@@ -118,7 +119,7 @@ class Carousel extends BaseComponent {
 
     this._config = this._getConfig(config)
     this._indicatorsElement = SelectorEngine.findOne(SELECTOR_INDICATORS, this._element)
-    this._touchSupported = 'ontouchstart' in document.documentElement || navigator.maxTouchPoints > 0
+    this._touchSupported = isTouchEnabledDevice() || navigator.maxTouchPoints > 0
     this._pointerEvent = Boolean(window.PointerEvent)
 
     this._addEventListeners()

js/src/dropdown.js

@@ -13,6 +13,7 @@ import {
   isElement,
   isVisible,
   isRTL,
+  isTouchEnabledDevice,
   noop,
   typeCheckConfig
 } from './util/index'
@@ -181,10 +182,10 @@ class Dropdown extends BaseComponent {
     // empty mouseover listeners to the body's immediate children;
     // only needed because of broken event delegation on iOS
     // https://www.quirksmode.org/blog/archives/2014/02/mouse_event_bub.html
-    if ('ontouchstart' in document.documentElement &&
-      !parent.closest(SELECTOR_NAVBAR_NAV)) {
-      [].concat(...document.body.children)
-        .forEach(elem => EventHandler.on(elem, 'mouseover', null, noop()))
+    if (isTouchEnabledDevice() && !parent.closest(SELECTOR_NAVBAR_NAV)) {
+      [].concat(...document.body.children).forEach(element => {
+        EventHandler.on(element, 'mouseover', null, noop)
+      })
     }
 
     this._element.focus()
@@ -381,9 +382,10 @@ class Dropdown extends BaseComponent {
 
       // If this is a touch-enabled device we remove the extra
       // empty mouseover listeners we added for iOS support
-      if ('ontouchstart' in document.documentElement) {
-        [].concat(...document.body.children)
-          .forEach(elem => EventHandler.off(elem, 'mouseover', null, noop()))
+      if (isTouchEnabledDevice()) {
+        [].concat(...document.body.children).forEach(element => {
+          EventHandler.off(element, 'mouseover', null, noop)
+        })
       }
 
       toggles[i].setAttribute('aria-expanded', 'false')

js/src/tooltip.js

@@ -16,6 +16,7 @@ import {
   getUID,
   isElement,
   isRTL,
+  isTouchEnabledDevice,
   noop,
   typeCheckConfig
 } from './util/index'
@@ -298,9 +299,9 @@ class Tooltip extends BaseComponent {
       // empty mouseover listeners to the body's immediate children;
       // only needed because of broken event delegation on iOS
       // https://www.quirksmode.org/blog/archives/2014/02/mouse_event_bub.html
-      if ('ontouchstart' in document.documentElement) {
+      if (isTouchEnabledDevice()) {
         [].concat(...document.body.children).forEach(element => {
-          EventHandler.on(element, 'mouseover', noop())
+          EventHandler.on(element, 'mouseover', noop)
         })
       }
 
@@ -355,9 +356,10 @@ class Tooltip extends BaseComponent {
 
     // If this is a touch-enabled device we remove the extra
     // empty mouseover listeners we added for iOS support
-    if ('ontouchstart' in document.documentElement) {
-      [].concat(...document.body.children)
-        .forEach(element => EventHandler.off(element, 'mouseover', noop))
+    if (isTouchEnabledDevice()) {
+      [].concat(...document.body.children).forEach(element => {
+        EventHandler.off(element, 'mouseover', noop)
+      })
     }
 
     this._activeTrigger[TRIGGER_CLICK] = false

js/src/util/index.js

@@ -204,6 +204,8 @@ const defineJQueryPlugin = (name, plugin) => {
   })
 }
 
+const isTouchEnabledDevice = () => 'ontouchstart' in document.documentElement
+
 export {
   TRANSITION_END,
   getUID,
@@ -221,5 +223,6 @@ export {
   getjQuery,
   onDOMContentLoaded,
   isRTL,
-  defineJQueryPlugin
+  defineJQueryPlugin,
+  isTouchEnabledDevice
 }