Switch to SafeObserver in MutationObserver classes to prevent errors …

…during SSR (#654)

libs/mutation-observer/src/classes/safe-observer.ts

@@ -0,0 +1,10 @@
+export const SafeObserver =
+    typeof MutationObserver !== `undefined`
+        ? MutationObserver
+        : class implements MutationObserver {
+              observe(): void {}
+              disconnect(): void {}
+              takeRecords(): MutationRecord[] {
+                  return [];
+              }
+          };

libs/mutation-observer/src/directives/mutation-observer.directive.ts

@@ -8,6 +8,7 @@ import {
     Output,
 } from '@angular/core';
 
+import {SafeObserver} from '../classes/safe-observer';
 import {MUTATION_OBSERVER_INIT} from '../tokens/mutation-observer-init';
 import {mutationObserverInitFactory} from '../utils/mutation-observer-init-factory';
 
@@ -22,7 +23,7 @@ import {mutationObserverInitFactory} from '../utils/mutation-observer-init-facto
         },
     ],
 })
-export class MutationObserverDirective extends MutationObserver implements OnDestroy {
+export class MutationObserverDirective extends SafeObserver implements OnDestroy {
     @Output()
     readonly waMutationObserver = new EventEmitter<MutationRecord[]>();
 

libs/mutation-observer/src/services/mutation-observer.service.ts

@@ -1,6 +1,7 @@
 import {ElementRef, Inject, Injectable} from '@angular/core';
 import {Observable} from 'rxjs';
 
+import {SafeObserver} from '../classes/safe-observer';
 import {MUTATION_OBSERVER_INIT} from '../tokens/mutation-observer-init';
 
 @Injectable()
@@ -10,7 +11,7 @@ export class MutationObserverService extends Observable<readonly MutationRecord[
         @Inject(MUTATION_OBSERVER_INIT) config: MutationObserverInit,
     ) {
         super(subscriber => {
-            const observer = new MutationObserver(records => {
+            const observer = new SafeObserver(records => {
                 subscriber.next(records);
             });