fix: check length only on unwrapped data

libs/ngu/carousel/src/lib/ngu-carousel/ngu-carousel.component.ts

@@ -11,7 +11,6 @@ import {
   EventEmitter,
   Inject,
   Input,
-  isDevMode,
   IterableChangeRecord,
   IterableChanges,
   IterableDiffer,
@@ -57,6 +56,14 @@ import { NguWindowScrollListener } from './ngu-window-scroll-listener';
 
 type DirectionSymbol = '' | '-';
 
+type NguCarouselDataSource = Observable<any[]> | any[] | null | undefined;
+
+// This will be provided through Terser global definitions by Angular CLI.
+// This is how Angular does tree-shaking internally.
+declare const ngDevMode: boolean;
+
+const NG_DEV_MODE = typeof ngDevMode === 'undefined' || ngDevMode;
+
 @Component({
   selector: 'ngu-carousel',
   templateUrl: 'ngu-carousel.component.html',
@@ -81,16 +88,26 @@ export class NguCarousel<T>
 
   private _arrayChanges: IterableChanges<{}> | null = null;
 
-  @Input('dataSource')
-  get dataSource(): any {
+  @Input()
+  get dataSource(): NguCarouselDataSource {
     return this._dataSource;
   }
-  set dataSource(data: any) {
+  set dataSource(data: NguCarouselDataSource) {
     if (data) {
       this._switchDataSource(data);
     }
   }
-  private _dataSource: any;
+  private _dataSource: NguCarouselDataSource = null;
+
+  /**
+   * `_dataSource` allows multiple values to be set considering nullable and
+   * observable values. We shouldn't try to get `_dataSource.length` since it
+   * might be `null|undefined` which will throw an error that property doesn't
+   * exist on `undefined`. It will also always equal `undefined` on observable.
+   * We should wait until the observable is unwrapped and then check the length
+   * of the actual unwrapped data.
+   */
+  private _unwrappedData: any[] = [];
 
   private _defaultNodeDef: NguCarouselDefDirective<any> | null;
 
@@ -156,7 +173,7 @@ export class NguCarousel<T>
     return this._trackByFn;
   }
   set trackBy(fn: TrackByFunction<T>) {
-    if (isDevMode() && fn != null && typeof fn !== 'function' && console && console.warn) {
+    if (NG_DEV_MODE && fn != null && typeof fn !== 'function' && console?.warn) {
       console.warn(`trackBy must be a function, but received ${JSON.stringify(fn)}.`);
     }
     this._trackByFn = fn;
@@ -181,13 +198,13 @@ export class NguCarousel<T>
   }
 
   ngOnInit() {
-    this._dataDiffer = this._differs.find([]).create((_i: number, item: any) => {
-      return this.trackBy ? this.trackBy(_i, item) : item;
-    });
+    this._dataDiffer = this._differs
+      .find([])
+      .create((index: number, item: any) => (this.trackBy ? this.trackBy(index, item) : item));
   }
 
   ngDoCheck() {
-    this._arrayChanges = this._dataDiffer.diff(this.dataSource)!;
+    this._arrayChanges = this._dataDiffer.diff(this._unwrappedData)!;
     if (this._arrayChanges && this._defDirectives) {
       this._observeRenderChanges();
     }
@@ -210,8 +227,9 @@ export class NguCarousel<T>
     }
 
     dataStream
-      ?.pipe(takeUntil(this._intervalController$), takeUntil(this._destroy$))
+      ?.pipe(takeUntil(merge(this._intervalController$, this._destroy$)))
       .subscribe(data => {
+        this._unwrappedData = data;
         this.renderNodeChanges(data);
         this.isLast = this._pointIndex === this.currentSlide;
       });
@@ -331,8 +349,6 @@ export class NguCarousel<T>
   ngOnDestroy() {
     this._hammertime?.destroy();
     this._destroy$.next();
-    this.carouselLoad.complete();
-    this.onMove.complete();
   }
 
   /** Get Touch input */
@@ -495,7 +511,7 @@ export class NguCarousel<T>
 
   /** Init carousel point */
   private _carouselPoint(): void {
-    const Nos = this.dataSource.length - (this.items - this.slideItems);
+    const Nos = this._unwrappedData.length - (this.items - this.slideItems);
     this._pointIndex = Math.ceil(Nos / this.slideItems);
     const pointers: number[] = [];
 
@@ -540,7 +556,7 @@ export class NguCarousel<T>
           break;
         case this._pointIndex - 1:
           this._btnBoolean(0, 1);
-          slideremains = this.dataSource.length - this.items;
+          slideremains = this._unwrappedData.length - this.items;
           break;
         default:
           this._btnBoolean(0, 0);
@@ -653,7 +669,7 @@ export class NguCarousel<T>
       const MoveSlide = currentSlideD + this.slideItems;
       this._btnBoolean(0, 1);
       if (this.currentSlide === 0) {
-        currentSlide = this.dataSource.length - this.items;
+        currentSlide = this._unwrappedData.length - this.items;
         itemSpeed = 400;
         this._btnBoolean(0, 1);
       } else if (this.slideItems >= MoveSlide) {
@@ -671,10 +687,10 @@ export class NguCarousel<T>
       this._carouselScrollTwo(Btn, currentSlide, itemSpeed);
     } else if (Btn === 1 && ((!this.loop && !this.isLast) || this.loop)) {
       if (
-        this.dataSource.length <= this.currentSlide + this.items + this.slideItems &&
+        this._unwrappedData.length <= this.currentSlide + this.items + this.slideItems &&
         !this.isLast
       ) {
-        currentSlide = this.dataSource.length - this.items;
+        currentSlide = this._unwrappedData.length - this.items;
         this._btnBoolean(0, 1);
       } else if (this.isLast) {
         currentSlide = 0;
@@ -720,7 +736,7 @@ export class NguCarousel<T>
       this._setStyle(this._nguItemsContainer.nativeElement, 'transition', ``);
     }
 
-    this.itemLength = this.dataSource.length;
+    this.itemLength = this._unwrappedData.length;
     this._transformStyle(currentSlide);
     this.currentSlide = currentSlide;
     this.onMove.emit(this);
@@ -773,7 +789,7 @@ export class NguCarousel<T>
   /** this will trigger the carousel to load the items */
   private _carouselLoadTrigger(): void {
     if (typeof this.inputs.load === 'number') {
-      this.dataSource.length - this.load <= this.currentSlide + this.items &&
+      this._unwrappedData.length - this.load <= this.currentSlide + this.items &&
         this.carouselLoad.emit(this.currentSlide);
     }
   }
@@ -944,4 +960,6 @@ export class NguCarousel<T>
         })
     );
   }
+
+  static ngAcceptInputType_dataSource: NguCarouselDataSource;
 }