feat(scroller): Enhance Scroller class with callback execution and adaptive scroll listener

ts/domtools.classes.scroller.ts

@@ -4,16 +4,32 @@ import * as plugins from './domtools.plugins.js';
 export class Scroller {
   public domtoolsInstance: DomTools;
 
-  constructor(
-    domtoolsInstanceArg: DomTools,
-  ) {
+  // Array to store scroll callback functions.
+  private scrollCallbacks: Array<() => void> = [];
+
+  // Lenis instance (if activated) or null.
+  private lenisInstance: plugins.Lenis | null = null;
+
+  // Bound handlers to allow removal from event listeners.
+  private handleNativeScroll = (event: Event): void => {
+    this.executeScrollCallbacks();
+  };
+
+  private handleLenisScroll = (info: any): void => {
+    this.executeScrollCallbacks();
+  };
+
+  constructor(domtoolsInstanceArg: DomTools) {
     this.domtoolsInstance = domtoolsInstanceArg;
+    // Attach the native scroll listener by default.
+    this.attachNativeScrollListener();
   }
 
-  private sweetScroller = new plugins.SweetScroll({
-    /* some options */
-  }); // TODO: switch to scroller class
+  private sweetScroller = new plugins.SweetScroll({});
 
+  /**
+   * Scrolls to a given element with options.
+   */
   public async scrollToElement(
     elementArg: HTMLElement,
     optionsArg: Parameters<typeof this.sweetScroller.toElement>[1]
@@ -22,6 +38,9 @@ export class Scroller {
     await plugins.smartdelay.delayFor(optionsArg.duration);
   }
 
+  /**
+   * Detects whether native smooth scrolling is enabled.
+   */
   public async detectNativeSmoothScroll() {
     const done = plugins.smartpromise.defer<boolean>();
     const sampleSize = 100;
@@ -64,14 +83,93 @@ export class Scroller {
     return done.promise;
   }
 
+  /**
+   * Enables Lenis scrolling.
+   * If optionsArg.disableOnNativeSmoothScroll is true and native smooth scrolling is detected,
+   * Lenis will be destroyed immediately.
+   */
   public async enableLenisScroll(optionsArg?: { disableOnNativeSmoothScroll?: boolean }) {
     const lenis = new plugins.Lenis({
       autoRaf: true,
     });
+
     if (optionsArg?.disableOnNativeSmoothScroll) {
       if (await this.detectNativeSmoothScroll()) {
         lenis.destroy();
+        return;
       }
     }
+
+    // Activate Lenis scrolling.
+    this.lenisInstance = lenis;
+    // Switch from native scroll listener to Lenis scroll listener.
+    this.detachNativeScrollListener();
+    this.attachLenisScrollListener();
+
+    // Monkey-patch the destroy method so that when Lenis is destroyed,
+    // the native scroll listener is reattached.
+    const originalDestroy = lenis.destroy.bind(lenis);
+    lenis.destroy = () => {
+      originalDestroy();
+      this.detachLenisScrollListener();
+      this.attachNativeScrollListener();
+      this.lenisInstance = null;
+    };
   }
-}
+
+  /**
+   * Registers a callback to be executed on scroll.
+   * @param callback A function to execute on each scroll event.
+   */
+  public onScroll(callback: () => void): void {
+    this.scrollCallbacks.push(callback);
+  }
+
+  /**
+   * Executes all registered scroll callbacks concurrently.
+   */
+  private executeScrollCallbacks(): void {
+    // Execute all callbacks in parallel.
+    this.scrollCallbacks.forEach((callback) => {
+      try {
+        callback();
+      } catch (error) {
+        console.error('Error in scroll callback:', error);
+      }
+    });
+  }
+
+  /**
+   * Attaches the native scroll event listener.
+   */
+  private attachNativeScrollListener(): void {
+    window.addEventListener('scroll', this.handleNativeScroll, { passive: true });
+  }
+
+  /**
+   * Detaches the native scroll event listener.
+   */
+  private detachNativeScrollListener(): void {
+    window.removeEventListener('scroll', this.handleNativeScroll);
+  }
+
+  /**
+   * Attaches the Lenis scroll event listener.
+   */
+  private attachLenisScrollListener(): void {
+    if (this.lenisInstance) {
+      // Assuming that Lenis exposes an `on` method to listen to scroll events.
+      this.lenisInstance.on('scroll', this.handleLenisScroll);
+    }
+  }
+
+  /**
+   * Detaches the Lenis scroll event listener.
+   */
+  private detachLenisScrollListener(): void {
+    if (this.lenisInstance) {
+      // Assuming that Lenis exposes an `off` method to remove scroll event listeners.
+      this.lenisInstance.off('scroll', this.handleLenisScroll);
+    }
+  }
+}