Use `Element.scrollIntoView`

Related to [@github/auto-complete-element#91][]

The current `scrollTo` helper method implementation can be unreliable
(or have no effect) at times.

This commit replaces it with a call to [Element.scrollIntoView][]. To
control that behavior, this commit also introduces a
`scrollIntoViewOptions:` key to the package's constructor call.

[@github/auto-complete-element#91]: https://github.com/github/auto-complete-element/issues/91
[Element.scrollIntoView]: https://developer.mozilla.org/en-US/docs/Web/API/Element/scrollIntoView
[ScrollIntoViewOptions]: https://developer.mozilla.org/en-US/docs/Web/API/Element/scrollIntoView#sect1

README.md

@@ -82,6 +82,12 @@ These settings are available:
 - `tabInsertsSuggestions: boolean = true` - Control whether the highlighted suggestion is inserted when <kbd>Tab</kbd> is pressed (<kbd>Enter</kbd> will always insert a suggestion regardless of this setting). When `true`, tab-navigation will be hijacked when open (which can have negative impacts on accessibility) but the combobox will more closely imitate a native IDE experience.
 - `defaultFirstOption: boolean = false` - If no options are selected and the user presses <kbd>Enter</kbd>, should the first item be inserted? If enabled, the default option can be selected and styled with `[data-combobox-option-default]` . This should be styled differently from the `aria-selected` option.
   > **Warning** Screen readers will not announce that the first item is the default. This should be announced explicitly with the use of `aria-live` status text.
+- `scrollIntoViewOptions?: boolean | ScrollIntoViewOptions = undefined` - When
+  controlling the element marked `[aria-selected="true"]` with keyboard navigation, the selected element will be scrolled into the viewport by a call to [Element.scrollIntoView][]. Configure this value to control the scrolling behavior (either with a `boolean` or a [ScrollIntoViewOptions][] object.
+
+[Element.scrollIntoView]: https://developer.mozilla.org/en-US/docs/Web/API/Element/scrollIntoView
+[ScrollIntoViewOptions]: https://developer.mozilla.org/en-US/docs/Web/API/Element/scrollIntoView#sect1
+
 
 ## Development
 

src/index.ts

@@ -1,6 +1,7 @@
 export type ComboboxSettings = {
   tabInsertsSuggestions?: boolean
   defaultFirstOption?: boolean
+  scrollIntoViewOptions?: boolean | ScrollIntoViewOptions
 }
 
 export default class Combobox {
@@ -13,16 +14,18 @@ export default class Combobox {
   ctrlBindings: boolean
   tabInsertsSuggestions: boolean
   defaultFirstOption: boolean
+  scrollIntoViewOptions?: boolean | ScrollIntoViewOptions
 
   constructor(
     input: HTMLTextAreaElement | HTMLInputElement,
     list: HTMLElement,
-    {tabInsertsSuggestions, defaultFirstOption}: ComboboxSettings = {}
+    {tabInsertsSuggestions, defaultFirstOption, scrollIntoViewOptions}: ComboboxSettings = {}
   ) {
     this.input = input
     this.list = list
     this.tabInsertsSuggestions = tabInsertsSuggestions ?? true
     this.defaultFirstOption = defaultFirstOption ?? false
+    this.scrollIntoViewOptions = scrollIntoViewOptions
 
     this.isComposing = false
 
@@ -107,7 +110,7 @@ export default class Combobox {
       if (target === el) {
         this.input.setAttribute('aria-activedescendant', target.id)
         target.setAttribute('aria-selected', 'true')
-        scrollTo(this.list, target)
+        target.scrollIntoView(this.scrollIntoViewOptions)
       } else {
         el.removeAttribute('aria-selected')
       }
@@ -204,17 +207,3 @@ function trackComposition(event: Event, combobox: Combobox): void {
 
   combobox.clearSelection()
 }
-
-function scrollTo(container: HTMLElement, target: HTMLElement) {
-  if (!inViewport(container, target)) {
-    container.scrollTop = target.offsetTop
-  }
-}
-
-function inViewport(container: HTMLElement, element: HTMLElement): boolean {
-  const scrollTop = container.scrollTop
-  const containerBottom = scrollTop + container.clientHeight
-  const top = element.offsetTop
-  const bottom = top + element.clientHeight
-  return top >= scrollTop && bottom <= containerBottom
-}