fix: [#2409] engine 'visible' event not firing

CHANGELOG.md

@@ -20,7 +20,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 
 ### Fixed
 
--
+- Fixed `engine.on('visible')` event not firing
 
 ### Updates
 

src/engine/Engine.ts

@@ -1109,24 +1109,11 @@ O|===|* >________________>\n\
     // Issue #385 make use of the visibility api
     // https://developer.mozilla.org/en-US/docs/Web/Guide/User_experience/Using_the_Page_Visibility_API
 
-    let hidden: keyof HTMLDocument, visibilityChange: string;
-    if (typeof document.hidden !== 'undefined') {
-      // Opera 12.10 and Firefox 18 and later support
-      hidden = 'hidden';
-      visibilityChange = 'visibilitychange';
-    } else if ('msHidden' in document) {
-      hidden = <keyof HTMLDocument>'msHidden';
-      visibilityChange = 'msvisibilitychange';
-    } else if ('webkitHidden' in document) {
-      hidden = <keyof HTMLDocument>'webkitHidden';
-      visibilityChange = 'webkitvisibilitychange';
-    }
-
-    this.browser.document.on(visibilityChange, () => {
-      if (document[hidden]) {
+    this.browser.document.on('visibilitychange', () => {
+      if (document.visibilityState === 'hidden') {
         this.eventDispatcher.emit('hidden', new HiddenEvent(this));
         this._logger.debug('Window hidden');
-      } else {
+      } else if (document.visibilityState === 'visible') {
         this.eventDispatcher.emit('visible', new VisibleEvent(this));
         this._logger.debug('Window visible');
       }

src/spec/EngineSpec.ts

@@ -397,6 +397,26 @@ describe('The engine', () => {
     expect(fired).toHaveBeenCalledTimes(2);
   });
 
+  it('should emit a visible event', () => {
+    const fired = jasmine.createSpy('fired');
+    engine.on('visible', fired);
+
+    spyOnProperty(window.document, 'visibilityState').and.returnValue('visible');
+    window.document.dispatchEvent(new CustomEvent('visibilitychange'));
+
+    expect(fired).toHaveBeenCalled();
+  });
+
+  it('should emit a hidden event', () => {
+    const fired = jasmine.createSpy('fired');
+    engine.on('hidden', fired);
+
+    spyOnProperty(window.document, 'visibilityState').and.returnValue('hidden');
+    window.document.dispatchEvent(new CustomEvent('visibilitychange'));
+
+    expect(fired).toHaveBeenCalled();
+  });
+
   it('should tell engine is running', () => {
     const status = engine.isRunning();
     expect(status).toBe(true);