set unmount event based on Turbolinks version

Author: William Meleyal

README.md

@@ -82,9 +82,9 @@ Component = React.createClass
 
 `react_ujs` will also scan DOM elements and call `React.unmountComponentAtNode` on page unload. If you want to disable this behavior, remove `data-react-class` attribute in `componentDidMount`.
 
-To use `react_ujs`, simply `require` it after `react` (and after `turbolinks` if [Turbolinks](https://github.com/rails/turbolinks) is used):
+To use `react_ujs`, simply `require` it after `react` (and after `turbolinks` if [Turbolinks](https://github.com/rails/turbolinks) is used).
 
-**Note:** _`react_ujs` disables the Turbolinks cache. This is a workaround to ensure components are correctly unmounted. See [#87](https://github.com/reactjs/react-rails/issues/87) for details._
+**Note:** _Turbolinks >= 2.4.0 is recommended. For older versions `react_ujs` will disable the Turbolinks cache to ensure components are correctly unmounted. See [#87](https://github.com/reactjs/react-rails/issues/87) for details._
 
 ```js
 // app/assets/javascripts/application.js

lib/assets/javascripts/react_ujs.js

@@ -38,9 +38,7 @@
 
   var handleTurbolinksEvents = function() {
     var handleEvent;
-
-    // Disable the Turbolinks cache.
-    Turbolinks.pagesCached(0);
+    var unmountEvent;
 
     if ($) {
       handleEvent = function(eventName, callback) {
@@ -51,8 +49,16 @@
         document.addEventListener(eventName, callback);
       }
     }
+
+    if (Turbolinks.EVENTS) {
+      unmountEvent = Turbolinks.EVENTS.BEFORE_UNLOAD;
+    } else {
+      unmountEvent = 'page:receive';
+      Turbolinks.pagesCached(0);
+    }
+
     handleEvent('page:change', mountReactComponents);
-    handleEvent('page:receive', unmountReactComponents);
+    handleEvent(unmountEvent, unmountReactComponents);
   };
 
   var handleNativeEvents = function() {