feat: Add platform browser detection to make library compatible with Angular Universal

Author: Marcus Williams

src/lib/src/ngx-lazy-load-images.directive.ts

@@ -1,5 +1,5 @@
-import { Directive, ElementRef, Renderer2, Input, NgZone } from '@angular/core';
-import 'intersection-observer';
+import { Directive, ElementRef, Renderer2, Input, NgZone, Inject, PLATFORM_ID } from '@angular/core';
+import { isPlatformBrowser } from '@angular/common';
 
 /**
  * Angular Lazy Loading Images Directive
@@ -18,10 +18,14 @@ export class LazyLoadImagesDirective {
   intersectionObserver: IntersectionObserver;
   rootElement: HTMLElement;
 
-  constructor(element: ElementRef, public renderer: Renderer2, public ngZone: NgZone) {
+  constructor(element: ElementRef, public renderer: Renderer2, public ngZone: NgZone, @Inject(PLATFORM_ID) private platformId: any) {
     this.rootElement = element.nativeElement;
   }
 
+  public get isBrowser(): boolean {
+    return isPlatformBrowser(this.platformId);
+  }
+
   init() {
     this.registerIntersectionObserver();
 
@@ -32,7 +36,10 @@ export class LazyLoadImagesDirective {
   }
 
   ngOnInit() {
-    this.ngZone.runOutsideAngular(() => this.init());
+    if (this.isBrowser) {
+      require('intersection-observer');
+      this.ngZone.runOutsideAngular(() => this.init());
+    }
   }
 
   ngOnDestroy() {