feat(version): versions

1 files changed, 131 insertions, 0 deletions

diff --git a/src/templates/assets/javascripts/browser/element/visibility/index.ts b/src/templates/assets/javascripts/browser/element/visibility/index.ts
new file mode 100644
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+++ b/src/templates/assets/javascripts/browser/element/visibility/index.ts
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+/*
+ * Copyright (c) 2016-2023 Martin Donath <martin.donath@squidfunk.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to
+ * deal in the Software without restriction, including without limitation the
+ * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+ * sell copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ */
+
+import {
+  NEVER,
+  Observable,
+  Subject,
+  defer,
+  distinctUntilChanged,
+  filter,
+  finalize,
+  map,
+  merge,
+  of,
+  shareReplay,
+  switchMap,
+  tap
+} from "rxjs"
+
+import {
+  getElementContentSize,
+  getElementSize,
+  watchElementContentOffset
+} from "~/browser"
+
+/* ----------------------------------------------------------------------------
+ * Data
+ * ------------------------------------------------------------------------- */
+
+/**
+ * Intersection observer entry subject
+ */
+const entry$ = new Subject<IntersectionObserverEntry>()
+
+/**
+ * Intersection observer observable
+ *
+ * This observable will create an `IntersectionObserver` on first subscription
+ * and will automatically terminate it when there are no more subscribers.
+ *
+ * @see https://bit.ly/3iIYfEm - Google Groups on performance
+ */
+const observer$ = defer(() => of(
+  new IntersectionObserver(entries => {
+    for (const entry of entries)
+      entry$.next(entry)
+  }, {
+    threshold: 0
+  })
+))
+  .pipe(
+    switchMap(observer => merge(NEVER, of(observer))
+      .pipe(
+        finalize(() => observer.disconnect())
+      )
+    ),
+    shareReplay(1)
+  )
+
+/* ----------------------------------------------------------------------------
+ * Functions
+ * ------------------------------------------------------------------------- */
+
+/**
+ * Watch element visibility
+ *
+ * @param el - Element
+ *
+ * @returns Element visibility observable
+ */
+export function watchElementVisibility(
+  el: HTMLElement
+): Observable<boolean> {
+  return observer$
+    .pipe(
+      tap(observer => observer.observe(el)),
+      switchMap(observer => entry$
+        .pipe(
+          filter(({ target }) => target === el),
+          finalize(() => observer.unobserve(el)),
+          map(({ isIntersecting }) => isIntersecting)
+        )
+      )
+    )
+}
+
+/**
+ * Watch element boundary
+ *
+ * This function returns an observable which emits whether the bottom content
+ * boundary (= scroll offset) of an element is within a certain threshold.
+ *
+ * @param el - Element
+ * @param threshold - Threshold
+ *
+ * @returns Element boundary observable
+ */
+export function watchElementBoundary(
+  el: HTMLElement, threshold = 16
+): Observable<boolean> {
+  return watchElementContentOffset(el)
+    .pipe(
+      map(({ y }) => {
+        const visible = getElementSize(el)
+        const content = getElementContentSize(el)
+        return y >= (
+          content.height - visible.height - threshold
+        )
+      }),
+      distinctUntilChanged()
+    )
+}