Change isTouchEnabledDevice to a function

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

js/src/carousel.js

@@ -119,7 +119,7 @@ class Carousel extends BaseComponent {
 
     this._config = this._getConfig(config)
     this._indicatorsElement = SelectorEngine.findOne(SELECTOR_INDICATORS, this._element)
-    this._touchSupported = isTouchEnabledDevice || navigator.maxTouchPoints > 0
+    this._touchSupported = isTouchEnabledDevice() || navigator.maxTouchPoints > 0
     this._pointerEvent = Boolean(window.PointerEvent)
 
     this._addEventListeners()

js/src/dropdown.js

@@ -182,7 +182,7 @@ 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 (isTouchEnabledDevice && !parent.closest(SELECTOR_NAVBAR_NAV)) {
+    if (isTouchEnabledDevice() && !parent.closest(SELECTOR_NAVBAR_NAV)) {
       [].concat(...document.body.children).forEach(element => {
         EventHandler.on(element, 'mouseover', null, noop)
       })
@@ -382,7 +382,7 @@ class Dropdown extends BaseComponent {
 
       // If this is a touch-enabled device we remove the extra
       // empty mouseover listeners we added for iOS support
-      if (isTouchEnabledDevice) {
+      if (isTouchEnabledDevice()) {
         [].concat(...document.body.children).forEach(element => {
           EventHandler.off(element, 'mouseover', null, noop)
         })

js/src/tooltip.js

@@ -299,7 +299,7 @@ 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 (isTouchEnabledDevice) {
+      if (isTouchEnabledDevice()) {
         [].concat(...document.body.children).forEach(element => {
           EventHandler.on(element, 'mouseover', noop)
         })
@@ -356,7 +356,7 @@ class Tooltip extends BaseComponent {
 
     // If this is a touch-enabled device we remove the extra
     // empty mouseover listeners we added for iOS support
-    if (isTouchEnabledDevice) {
+    if (isTouchEnabledDevice()) {
       [].concat(...document.body.children).forEach(element => {
         EventHandler.off(element, 'mouseover', noop)
       })

js/src/util/index.js

@@ -204,7 +204,7 @@ const defineJQueryPlugin = (name, plugin) => {
   })
 }
 
-const isTouchEnabledDevice = 'ontouchstart' in document.documentElement
+const isTouchEnabledDevice = () => 'ontouchstart' in document.documentElement
 
 export {
   TRANSITION_END,