Testing addition of pseudo page visibility API

assets/scripts/modules/AbstractModule.js

@@ -1,10 +1,11 @@
+/* jshint esnext: true */
 import { $document, $window, $html, $body } from '../utils/environment';
 
 /**
  * Abstract module
  * Gives access to generic jQuery nodes
  */
-class AbstractModule {
+export default class {
 	constructor(options) {
 		this.$document = $document;
 		this.$window = $window;
@@ -13,5 +14,3 @@ class AbstractModule {
 		this.$el = options.$el;
 	}
 }
-
-export default AbstractModule;

assets/scripts/modules/Title.js

@@ -1,4 +1,5 @@
 /* jshint esnext: true */
+import { registerDocumentHiddenCallback, registerDocumentVisibleCallback } from '../utils/visibility';
 import AbstractModule from './AbstractModule';
 
 export default class extends AbstractModule {
@@ -10,6 +11,17 @@ export default class extends AbstractModule {
 		this.$document.on('title.changeLabel', (event, value) => {
 			this.changeLabel(value);
 		});
+
+		registerDocumentHiddenCallback(this.logHidden);
+		registerDocumentVisibleCallback(this.logVisible);
+	}
+
+	logHidden() {
+		console.log('Title is hidden');
+	}
+
+	logVisible() {
+		console.log('Title is visible');
 	}
 
 	changeLabel(value) {

assets/scripts/utils/visibility.js

@@ -0,0 +1,36 @@
+/* jshint esnext: true */
+import { $document, $window, $html, $body } from '../utils/environment';
+
+const CALLBACKS = {
+	hidden: [],
+	visible: []
+};
+
+// Main event
+$document.on('visibilitychange', function(event) {
+	if(document.hidden){
+		onDocumentChange('hidden');
+	}else{
+		onDocumentChange('visible');
+	}
+});
+
+function registerDocumentHiddenCallback(callback) {
+	CALLBACKS['hidden'].push(callback);
+}
+
+function registerDocumentVisibleCallback(callback) {
+	CALLBACKS['visible'].push(callback);
+}
+
+function onDocumentChange(state) {
+	let callbacks = CALLBACKS[state];
+	let i = 0;
+	let len = callbacks.length;
+
+	for (; i < len; i++) {
+		callbacks[i]();
+	}
+}
+
+export {registerDocumentHiddenCallback, registerDocumentVisibleCallback};