feat(version): versions

11 files changed, 793 insertions, 0 deletions

diff --git a/src/templates/assets/javascripts/browser/element/_/.eslintrc b/src/templates/assets/javascripts/browser/element/_/.eslintrc
new file mode 100644
index 00000000..16973760
--- /dev/null
+++ b/src/templates/assets/javascripts/browser/element/_/.eslintrc
@@ -0,0 +1,6 @@
+{
+  "rules": {
+    "jsdoc/require-jsdoc": "off",
+    "jsdoc/require-returns-check": "off"
+  }
+}
diff --git a/src/templates/assets/javascripts/browser/element/_/index.ts b/src/templates/assets/javascripts/browser/element/_/index.ts
new file mode 100644
index 00000000..b7beb462
--- /dev/null
+++ b/src/templates/assets/javascripts/browser/element/_/index.ts
@@ -0,0 +1,120 @@
+/*
+ * 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.
+ */
+
+/* ----------------------------------------------------------------------------
+ * Functions
+ * ------------------------------------------------------------------------- */
+
+/**
+ * Retrieve all elements matching the query selector
+ *
+ * @template T - Element type
+ *
+ * @param selector - Query selector
+ * @param node - Node of reference
+ *
+ * @returns Elements
+ */
+export function getElements<T extends keyof HTMLElementTagNameMap>(
+  selector: T, node?: ParentNode
+): HTMLElementTagNameMap[T][]
+
+export function getElements<T extends HTMLElement>(
+  selector: string, node?: ParentNode
+): T[]
+
+export function getElements<T extends HTMLElement>(
+  selector: string, node: ParentNode = document
+): T[] {
+  return Array.from(node.querySelectorAll<T>(selector))
+}
+
+/**
+ * Retrieve an element matching a query selector or throw a reference error
+ *
+ * Note that this function assumes that the element is present. If unsure if an
+ * element is existent, use the `getOptionalElement` function instead.
+ *
+ * @template T - Element type
+ *
+ * @param selector - Query selector
+ * @param node - Node of reference
+ *
+ * @returns Element
+ */
+export function getElement<T extends keyof HTMLElementTagNameMap>(
+  selector: T, node?: ParentNode
+): HTMLElementTagNameMap[T]
+
+export function getElement<T extends HTMLElement>(
+  selector: string, node?: ParentNode
+): T
+
+export function getElement<T extends HTMLElement>(
+  selector: string, node: ParentNode = document
+): T {
+  const el = getOptionalElement<T>(selector, node)
+  if (typeof el === "undefined")
+    throw new ReferenceError(
+      `Missing element: expected "${selector}" to be present`
+    )
+
+  /* Return element */
+  return el
+}
+
+/* ------------------------------------------------------------------------- */
+
+/**
+ * Retrieve an optional element matching the query selector
+ *
+ * @template T - Element type
+ *
+ * @param selector - Query selector
+ * @param node - Node of reference
+ *
+ * @returns Element or nothing
+ */
+export function getOptionalElement<T extends keyof HTMLElementTagNameMap>(
+  selector: T, node?: ParentNode
+): HTMLElementTagNameMap[T] | undefined
+
+export function getOptionalElement<T extends HTMLElement>(
+  selector: string, node?: ParentNode
+): T | undefined
+
+export function getOptionalElement<T extends HTMLElement>(
+  selector: string, node: ParentNode = document
+): T | undefined {
+  return node.querySelector<T>(selector) || undefined
+}
+
+/**
+ * Retrieve the currently active element
+ *
+ * @returns Element or nothing
+ */
+export function getActiveElement(): HTMLElement | undefined {
+  return document.activeElement instanceof HTMLElement
+    ? document.activeElement || undefined
+    : undefined
+}
diff --git a/src/templates/assets/javascripts/browser/element/focus/index.ts b/src/templates/assets/javascripts/browser/element/focus/index.ts
new file mode 100644
index 00000000..f31fe276
--- /dev/null
+++ b/src/templates/assets/javascripts/browser/element/focus/index.ts
@@ -0,0 +1,81 @@
+/*
+ * 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 {
+  Observable,
+  debounceTime,
+  distinctUntilChanged,
+  fromEvent,
+  map,
+  merge,
+  shareReplay,
+  startWith
+} from "rxjs"
+
+import { getActiveElement } from "../_"
+
+/* ----------------------------------------------------------------------------
+ * Data
+ * ------------------------------------------------------------------------- */
+
+/**
+ * Focus observable
+ *
+ * Previously, this observer used `focus` and `blur` events to determine whether
+ * an element is focused, but this doesn't work if there are focusable elements
+ * within the elements itself. A better solutions are `focusin` and `focusout`
+ * events, which bubble up the tree and allow for more fine-grained control.
+ *
+ * `debounceTime` is necessary, because when a focus change happens inside an
+ * element, the observable would first emit `false` and then `true` again.
+ */
+const observer$ = merge(
+  fromEvent(document.body, "focusin"),
+  fromEvent(document.body, "focusout")
+)
+  .pipe(
+    debounceTime(1),
+    startWith(undefined),
+    map(() => getActiveElement() || document.body),
+    shareReplay(1)
+  )
+
+/* ----------------------------------------------------------------------------
+ * Functions
+ * ------------------------------------------------------------------------- */
+
+/**
+ * Watch element focus
+ *
+ * @param el - Element
+ *
+ * @returns Element focus observable
+ */
+export function watchElementFocus(
+  el: HTMLElement
+): Observable<boolean> {
+  return observer$
+    .pipe(
+      map(active => el.contains(active)),
+      distinctUntilChanged()
+    )
+}
diff --git a/src/templates/assets/javascripts/browser/element/index.ts b/src/templates/assets/javascripts/browser/element/index.ts
new file mode 100644
index 00000000..50ce84b2
--- /dev/null
+++ b/src/templates/assets/javascripts/browser/element/index.ts
@@ -0,0 +1,27 @@
+/*
+ * 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.
+ */
+
+export * from "./_"
+export * from "./focus"
+export * from "./offset"
+export * from "./size"
+export * from "./visibility"
diff --git a/src/templates/assets/javascripts/browser/element/offset/_/index.ts b/src/templates/assets/javascripts/browser/element/offset/_/index.ts
new file mode 100644
index 00000000..6dd229d5
--- /dev/null
+++ b/src/templates/assets/javascripts/browser/element/offset/_/index.ts
@@ -0,0 +1,86 @@
+/*
+ * 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 {
+  Observable,
+  animationFrameScheduler,
+  auditTime,
+  fromEvent,
+  map,
+  merge,
+  startWith
+} from "rxjs"
+
+/* ----------------------------------------------------------------------------
+ * Types
+ * ------------------------------------------------------------------------- */
+
+/**
+ * Element offset
+ */
+export interface ElementOffset {
+  x: number                            /* Horizontal offset */
+  y: number                            /* Vertical offset */
+}
+
+/* ----------------------------------------------------------------------------
+ * Functions
+ * ------------------------------------------------------------------------- */
+
+/**
+ * Retrieve element offset
+ *
+ * @param el - Element
+ *
+ * @returns Element offset
+ */
+export function getElementOffset(
+  el: HTMLElement
+): ElementOffset {
+  return {
+    x: el.offsetLeft,
+    y: el.offsetTop
+  }
+}
+
+/* ------------------------------------------------------------------------- */
+
+/**
+ * Watch element offset
+ *
+ * @param el - Element
+ *
+ * @returns Element offset observable
+ */
+export function watchElementOffset(
+  el: HTMLElement
+): Observable<ElementOffset> {
+  return merge(
+    fromEvent(window, "load"),
+    fromEvent(window, "resize")
+  )
+    .pipe(
+      auditTime(0, animationFrameScheduler),
+      map(() => getElementOffset(el)),
+      startWith(getElementOffset(el))
+    )
+}
diff --git a/src/templates/assets/javascripts/browser/element/offset/content/index.ts b/src/templates/assets/javascripts/browser/element/offset/content/index.ts
new file mode 100644
index 00000000..557301a6
--- /dev/null
+++ b/src/templates/assets/javascripts/browser/element/offset/content/index.ts
@@ -0,0 +1,76 @@
+/*
+ * 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 {
+  Observable,
+  animationFrameScheduler,
+  auditTime,
+  fromEvent,
+  map,
+  merge,
+  startWith
+} from "rxjs"
+
+import { ElementOffset } from "../_"
+
+/* ----------------------------------------------------------------------------
+ * Functions
+ * ------------------------------------------------------------------------- */
+
+/**
+ * Retrieve element content offset (= scroll offset)
+ *
+ * @param el - Element
+ *
+ * @returns Element content offset
+ */
+export function getElementContentOffset(
+  el: HTMLElement
+): ElementOffset {
+  return {
+    x: el.scrollLeft,
+    y: el.scrollTop
+  }
+}
+
+/* ------------------------------------------------------------------------- */
+
+/**
+ * Watch element content offset
+ *
+ * @param el - Element
+ *
+ * @returns Element content offset observable
+ */
+export function watchElementContentOffset(
+  el: HTMLElement
+): Observable<ElementOffset> {
+  return merge(
+    fromEvent(el, "scroll"),
+    fromEvent(window, "resize")
+  )
+    .pipe(
+      auditTime(0, animationFrameScheduler),
+      map(() => getElementContentOffset(el)),
+      startWith(getElementContentOffset(el))
+    )
+}
diff --git a/src/templates/assets/javascripts/browser/element/offset/index.ts b/src/templates/assets/javascripts/browser/element/offset/index.ts
new file mode 100644
index 00000000..602ff2cf
--- /dev/null
+++ b/src/templates/assets/javascripts/browser/element/offset/index.ts
@@ -0,0 +1,24 @@
+/*
+ * 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.
+ */
+
+export * from "./_"
+export * from "./content"
diff --git a/src/templates/assets/javascripts/browser/element/size/_/index.ts b/src/templates/assets/javascripts/browser/element/size/_/index.ts
new file mode 100644
index 00000000..35a5e68b
--- /dev/null
+++ b/src/templates/assets/javascripts/browser/element/size/_/index.ts
@@ -0,0 +1,151 @@
+/*
+ * 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,
+  filter,
+  finalize,
+  map,
+  merge,
+  of,
+  shareReplay,
+  startWith,
+  switchMap,
+  tap
+} from "rxjs"
+
+import { watchScript } from "../../../script"
+
+/* ----------------------------------------------------------------------------
+ * Types
+ * ------------------------------------------------------------------------- */
+
+/**
+ * Element offset
+ */
+export interface ElementSize {
+  width: number                        /* Element width */
+  height: number                       /* Element height */
+}
+
+/* ----------------------------------------------------------------------------
+ * Data
+ * ------------------------------------------------------------------------- */
+
+/**
+ * Resize observer entry subject
+ */
+const entry$ = new Subject<ResizeObserverEntry>()
+
+/**
+ * Resize observer observable
+ *
+ * This observable will create a `ResizeObserver` on the first subscription
+ * and will automatically terminate it when there are no more subscribers.
+ * It's quite important to centralize observation in a single `ResizeObserver`,
+ * as the performance difference can be quite dramatic, as the link shows.
+ *
+ * If the browser doesn't have a `ResizeObserver` implementation available, a
+ * polyfill is automatically downloaded from unpkg.com. This is also compatible
+ * with the built-in privacy plugin, which will download the polyfill and put
+ * it alongside the built site for self-hosting.
+ *
+ * @see https://bit.ly/3iIYfEm - Google Groups on performance
+ */
+const observer$ = defer(() => (
+  typeof ResizeObserver === "undefined"
+    ? watchScript("https://unpkg.com/resize-observer-polyfill")
+    : of(undefined)
+))
+  .pipe(
+    map(() => new ResizeObserver(entries => {
+      for (const entry of entries)
+        entry$.next(entry)
+    })),
+    switchMap(observer => merge(NEVER, of(observer))
+      .pipe(
+        finalize(() => observer.disconnect())
+      )
+    ),
+    shareReplay(1)
+  )
+
+/* ----------------------------------------------------------------------------
+ * Functions
+ * ------------------------------------------------------------------------- */
+
+/**
+ * Retrieve element size
+ *
+ * @param el - Element
+ *
+ * @returns Element size
+ */
+export function getElementSize(
+  el: HTMLElement
+): ElementSize {
+  return {
+    width:  el.offsetWidth,
+    height: el.offsetHeight
+  }
+}
+
+/* ------------------------------------------------------------------------- */
+
+/**
+ * Watch element size
+ *
+ * This function returns an observable that subscribes to a single internal
+ * instance of `ResizeObserver` upon subscription, and emit resize events until
+ * termination. Note that this function should not be called with the same
+ * element twice, as the first unsubscription will terminate observation.
+ *
+ * Sadly, we can't use the `DOMRect` objects returned by the observer, because
+ * we need the emitted values to be consistent with `getElementSize`, which will
+ * return the used values (rounded) and not actual values (unrounded). Thus, we
+ * use the `offset*` properties. See the linked GitHub issue.
+ *
+ * @see https://bit.ly/3m0k3he - GitHub issue
+ *
+ * @param el - Element
+ *
+ * @returns Element size observable
+ */
+export function watchElementSize(
+  el: HTMLElement
+): Observable<ElementSize> {
+  return observer$
+    .pipe(
+      tap(observer => observer.observe(el)),
+      switchMap(observer => entry$
+        .pipe(
+          filter(({ target }) => target === el),
+          finalize(() => observer.unobserve(el)),
+          map(() => getElementSize(el))
+        )
+      ),
+      startWith(getElementSize(el))
+    )
+}
diff --git a/src/templates/assets/javascripts/browser/element/size/content/index.ts b/src/templates/assets/javascripts/browser/element/size/content/index.ts
new file mode 100644
index 00000000..5ed388cf
--- /dev/null
+++ b/src/templates/assets/javascripts/browser/element/size/content/index.ts
@@ -0,0 +1,67 @@
+/*
+ * 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 { ElementSize } from "../_"
+
+/* ----------------------------------------------------------------------------
+ * Functions
+ * ------------------------------------------------------------------------- */
+
+/**
+ * Retrieve element content size (= scroll width and height)
+ *
+ * @param el - Element
+ *
+ * @returns Element content size
+ */
+export function getElementContentSize(
+  el: HTMLElement
+): ElementSize {
+  return {
+    width:  el.scrollWidth,
+    height: el.scrollHeight
+  }
+}
+
+/**
+ * Retrieve the overflowing container of an element, if any
+ *
+ * @param el - Element
+ *
+ * @returns Overflowing container or nothing
+ */
+export function getElementContainer(
+  el: HTMLElement
+): HTMLElement | undefined {
+  let parent = el.parentElement
+  while (parent)
+    if (
+      el.scrollWidth  <= parent.scrollWidth &&
+      el.scrollHeight <= parent.scrollHeight
+    )
+      parent = (el = parent).parentElement
+    else
+      break
+
+  /* Return overflowing container */
+  return parent ? el : undefined
+}
diff --git a/src/templates/assets/javascripts/browser/element/size/index.ts b/src/templates/assets/javascripts/browser/element/size/index.ts
new file mode 100644
index 00000000..602ff2cf
--- /dev/null
+++ b/src/templates/assets/javascripts/browser/element/size/index.ts
@@ -0,0 +1,24 @@
+/*
+ * 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.
+ */
+
+export * from "./_"
+export * from "./content"
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
index 00000000..1ffe0b8d
--- /dev/null
+++ b/src/templates/assets/javascripts/browser/element/visibility/index.ts
@@ -0,0 +1,131 @@
+/*
+ * 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()
+    )
+}