Try sidemenu with internal observable

frontend/src/app/shared/components/sidemenu/sidemenu.component.html

@@ -1,26 +1,29 @@
-<button
-  class="op-sidemenu--title"
-  type="button"
-  (click)="toggleCollapsed()"
-  *ngIf="title && collapsible"
->
-  <span class="icon3 icon-small"
-        [ngClass]="collapsed ? 'icon-arrow-down1' : 'icon-arrow-up1'"
-        aria-hidden="true">
-  </span>
-  {{ title }}
-</button>
+<ng-container *ngIf="{collapsed: (collapsed$ | async)} as observables">
+  <button
+    *ngIf="title && collapsible"
+    class="op-sidemenu--title"
+    type="button"
+    (click)="collapsed$.next(!observables.collapsed)"
+  >
+    <span
+      class="icon3 icon-small"
+      [ngClass]="(collapsed$ | async) ? 'icon-arrow-down1' : 'icon-arrow-up1'"
+      aria-hidden="true"
+    ></span>
+    {{ title }}
+  </button>
+</ng-container>
 
 <div
-  class="op-sidemenu--title"
   *ngIf="title && !collapsible"
+  class="op-sidemenu--title"
 >
   {{ title }}
 </div>
 
 <ul
   class="op-sidemenu--items"
-  [ngClass]="{'op-sidemenu--items_collapsed' : collapsed}"
+  [ngClass]="{'op-sidemenu--items_collapsed': (collapsed$ | async)}"
 >
   <li
     class="op-sidemenu--item"

frontend/src/app/shared/components/sidemenu/sidemenu.component.ts

@@ -1,11 +1,10 @@
 import {
   ChangeDetectionStrategy,
-  ChangeDetectorRef,
   Component,
   Input,
   HostBinding,
 } from '@angular/core';
-import { I18nService } from 'core-app/core/i18n/i18n.service';
+import { Subject } from 'rxjs';
 
 export interface IOpSidemenuItem {
   title:string;
@@ -27,21 +26,15 @@ export interface IOpSidemenuItem {
 export class OpSidemenuComponent {
   @HostBinding('class.op-sidemenu') className = true;
 
-  @HostBinding('class.op-sidemenu_collapsed') collapsed = false;
-
   @Input() items:IOpSidemenuItem[] = [];
 
   @Input() title:string;
 
   @Input() collapsible = true;
 
-  constructor(
-    readonly cdRef:ChangeDetectorRef,
-    readonly I18n:I18nService,
-  ) {
-  }
+  public collapsed$ = new Subject();
 
-  toggleCollapsed():void {
-    this.collapsed = !this.collapsed;
+  constructor() {
+    this.collapsed$.next(false);
   }
 }