katja's git: oeffisearch

baseView: add `isOffline` state variable

diff --git a/src/baseView.js b/src/baseView.js
@@ -5,6 +5,7 @@ import { baseStyles, helperStyles, flexboxStyles, overlaysStyles, buttonInputSty
 
 export class BaseView extends LitElement {
 	static properties = {
+		isOffline:      { state: true },
 		isUpdating:     { state: true },
 		overlayType:    { state: true },
 		overlayTitle:   { state: true },

@@ -24,6 +25,7 @@ export class BaseView extends LitElement {
 	constructor () {
 		super();
 
+		this.isOffline  = !navigator.onLine;
 		this.isUpdating = false;
 
 		this.overlayType    = 'plain';

@@ -32,6 +34,20 @@ export class BaseView extends LitElement {
 		this.overlayTitle   = null;
 	}
 
+	connectedCallback() {
+		super.connectedCallback();
+		window.addEventListener('online',  this.connectionHandler);
+		window.addEventListener('offline', this.connectionHandler);
+	}
+
+	disconnectedCallback() {
+		super.disconnectedCallback();
+		window.removeEventListener('online',  this.connectionHandler);
+		window.removeEventListener('offline', this.connectionHandler);
+	}
+
+	connectionHandler = event => { this.isOffline = event.type === 'offline'; };
+
 	showLoaderOverlay = ()            => this.showOverlay('loader');
 	showDialogOverlay = (title, body) => this.showOverlay('dialog', body, title);
 	showAlertOverlay  = text          => this.showOverlay('alert', text);