Allow init chaining

js/src/chartviewmodel.js

@@ -60,10 +60,14 @@ export default class ChartViewModel extends ViewModel {
     this.buttonElement = document.querySelector('#altitudes');
   }
 
+  /**
+   * @return {ChartViewModel}
+   */
   init() {
     this.chartSetup();
     this.setObservers();
     this.bindAll();
+    return this;
   }
 
   chartSetup() {

js/src/configviewmodel.js

@@ -34,9 +34,13 @@ export default class ConfigViewModel extends ViewModel {
     this.model.onSetInterval = () => this.setAutoReloadInterval();
   }
 
+  /**
+   * @return {ConfigViewModel}
+   */
   init() {
     this.setObservers();
     this.bindAll();
+    return this;
   }
 
   setObservers() {

js/src/mainviewmodel.js

@@ -39,8 +39,12 @@ export default class MainViewModel extends ViewModel {
     this.userMenuEl = document.querySelector('#user-menu');
   }
 
+  /**
+   * @return {MainViewModel}
+   */
   init() {
     this.bindAll();
+    return this;
   }
 
   toggleSideMenu() {

js/src/mapviewmodel.js

@@ -64,9 +64,13 @@ export default class MapViewModel extends ViewModel {
     this.api = null;
   }
 
+  /**
+   * @return {MapViewModel}
+   */
   init() {
     this.bindAll();
     this.setObservers();
+    return this;
   }
 
   /**

js/src/trackviewmodel.js

@@ -66,9 +66,13 @@ export default class TrackViewModel extends ViewModel {
     this.timerId = 0;
   }
 
+  /**
+   * @return {TrackViewModel}
+   */
   init() {
     this.setObservers();
     this.bindAll();
+    return this;
   }
 
   setObservers() {

js/src/userviewmodel.js

@@ -44,6 +44,9 @@ export default class UserViewModel extends ViewModel {
     this.state = state;
   }
 
+  /**
+   * @return {UserViewModel}
+   */
   init() {
     this.setObservers(this.state);
     this.bindAll();
@@ -62,6 +65,7 @@ export default class UserViewModel extends ViewModel {
       }
     })
       .catch((e) => { uUtils.error(e, `${$._('actionfailure')}\n${e.message}`); });
+    return this;
   }
 
   /**