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* @module Watchers/ScrollWatcher
*/
import * as MC from "@lisn/globals/minification-constants";
import * as MH from "@lisn/globals/minification-helpers";
import { XYDirection, ScrollDirection, SizeTarget } from "@lisn/globals/types";
import {
ScrollTarget,
TargetCoordinate,
TargetCoordinates,
CommaSeparatedStr,
} from "@lisn/globals/types";
import { setNumericStyleJsVars } from "@lisn/utils/css-alter";
import { getMaxDeltaDirection } from "@lisn/utils/directions";
import { moveElement, tryWrapContent } from "@lisn/utils/dom-alter";
import { waitForMeasureTime } from "@lisn/utils/dom-optimize";
import { addEventListenerTo, removeEventListenerFrom } from "@lisn/utils/event";
import { logError } from "@lisn/utils/log";
import { toNonNegNum, maxAbs } from "@lisn/utils/math";
import {
scrollTo,
getCurrentScrollAction,
getClientWidthNow,
getClientHeightNow,
tryGetMainScrollableElement,
fetchMainContentElement,
fetchMainScrollableElement,
fetchScrollableElement,
isValidScrollDirection,
ScrollAction,
ScrollToOptions,
} from "@lisn/utils/scroll";
import { objToStrKey } from "@lisn/utils/text";
import { validateStrList } from "@lisn/utils/validation";
import {
CallbackHandler,
Callback,
wrapCallback,
} from "@lisn/modules/callback";
import { newXWeakMap } from "@lisn/modules/x-map";
import { MutationOperation, DOMWatcher } from "@lisn/watchers/dom-watcher";
import { SizeWatcher } from "@lisn/watchers/size-watcher";
import debug from "@lisn/debug/debug";
// re-export for convenience
export type { ScrollAction, ScrollToOptions } from "@lisn/utils/scroll";
/**
* {@link ScrollWatcher} listens for scroll events in any direction.
*
* It manages registered callbacks globally and reuses event listeners for more
* efficient performance.
*/
export class ScrollWatcher {
/**
* Call the given handler whenever the given scrollable is scrolled.
*
* Unless {@link OnScrollOptions.skipInitial} is true, the handler is also
* called (almost) immediately with the latest scroll data. If a scroll has
* not yet been observed on the scrollable and its `scrollTop` and
* `scrollLeft` are 0, then the direction is {@link Types.NoDirection} and
* the handler is only called if {@link Types.NoDirection} is part of the
* supplied {@link OnScrollOptions.directions | options.directions} (or
* {@link OnScrollOptions.directions | options.directions} is not given).
*
* **IMPORTANT:** The same handler can _not_ be added multiple times for the
* same scrollable, even if the options differ. If the handler has already
* been added for this scrollable, either using {@link trackScroll} or using
* {@link onScroll}, then it will be removed and re-added with the current
* options. So if previously it was also tracking content size changes using
* {@link trackScroll}, it will no longer do so.
*
* @throws {@link Errors.LisnUsageError | LisnUsageError}
* If the options are invalid.
*/
readonly onScroll: (
handler: OnScrollHandler,
options?: OnScrollOptions,
) => Promise<void>;
/**
* Removes a previously added handler.
*
* @throws {@link Errors.LisnUsageError | LisnUsageError}
* If the scrollable is invalid.
*/
readonly offScroll: (
handler: OnScrollHandler,
scrollable?: ScrollTarget,
) => void;
/**
* This everything that {@link onScroll} does plus more:
*
* In addition to a scroll event, the handler is also called when either the
* offset size or scroll (content) size of the scrollable changes as that
* would affect its `scrollTopFraction` and `scrollLeftFraction` and possibly
* the `scrollTop` and `scrollLeft` as well.
*
* **IMPORTANT:** The same handler can _not_ be added multiple times for the
* same scrollable, even if the options differ. If the handler has already
* been added for this scrollable, either using {@link trackScroll} or using
* {@link onScroll}, then it will be removed and re-added with the current
* options.
*
* ------
*
* If `handler` is not given, then it defaults to an internal handler that
* updates a set of CSS variables on the scrollable element's style:
*
* - If {@link OnScrollOptions.scrollable | options.scrollable} is not given,
* or is `null`, `window` or `document`, the following CSS variables are
* set on the root (`html`) element and represent the scroll of the
* {@link Settings.settings.mainScrollableElementSelector | the main scrolling element}:
* - `--lisn-js--page-scroll-top`
* - `--lisn-js--page-scroll-top-fraction`
* - `--lisn-js--page-scroll-left`
* - `--lisn-js--page-scroll-left-fraction`
* - `--lisn-js--page-scroll-width`
* - `--lisn-js--page-scroll-height`
*
* - Otherwise, the following variables are set on the scrollable itself,
* and represent its scroll offset:
* - `--lisn-js--scroll-top`
* - `--lisn-js--scroll-top-fraction`
* - `--lisn-js--scroll-left`
* - `--lisn-js--scroll-left-fraction`
* - `--lisn-js--scroll-width`
* - `--lisn-js--scroll-height`
*
* @throws {@link Errors.LisnUsageError | LisnUsageError}
* If the options are invalid.
*/
readonly trackScroll: (
handler?: OnScrollHandler | null,
options?: OnScrollOptions,
) => Promise<void>;
/**
* Removes a previously added handler for {@link trackScroll}.
*
* @throws {@link Errors.LisnUsageError | LisnUsageError}
* If the scrollable is invalid.
*/
readonly noTrackScroll: (
handler?: OnScrollHandler | null,
scrollable?: ScrollTarget,
) => void;
/**
* Get the scroll offset of the given scrollable. By default, it will
* {@link waitForMeasureTime} and so will be delayed by one frame.
*
* @param realtime If true, it will not {@link waitForMeasureTime}. Use
* this only when doing realtime scroll-based animations
* as it may cause a forced layout.
*
* @throws {@link Errors.LisnUsageError | LisnUsageError}
* If the scrollable is invalid.
*/
readonly fetchCurrentScroll: (
scrollable?: ScrollTarget,
realtime?: boolean,
) => Promise<ScrollData>;
/**
* Scrolls the given scrollable element to in the given direction.
*
* @throws {@link Errors.LisnUsageError | LisnUsageError}
* If the direction or options are invalid.
*/
readonly scroll: (
direction: XYDirection,
options?: ScrollOptions,
) => Promise<ScrollAction | null>;
/**
* Scrolls the given scrollable element to the given `to` scrollable.
*
* Returns `null` if there's an ongoing scroll that is not cancellable.
*
* Note that if `to` is an element or a selector, then it _must_ be a
* descendant of the scrollable element.
*
* @throws {@link Errors.LisnUsageError | LisnUsageError}
* If the "to" coordinates or options are invalid.
*
* @param to If this is an element, then its top-left position is used as
* the target coordinates. If it is a string, then it is treated
* as a selector for an element using `querySelector`.
* @param [options.scrollable]
* If not given, it defaults to
* {@link Settings.settings.mainScrollableElementSelector | the main scrolling element}.
*
* @returns `null` if there's an ongoing scroll that is not cancellable,
* otherwise a {@link ScrollAction}.
*/
readonly scrollTo: (
to: TargetCoordinates | Element | string,
options?: ScrollToOptions,
) => Promise<ScrollAction | null>;
/**
* Returns the current {@link ScrollAction} if any.
*
* @param scrollable If not given, it defaults to
* {@link Settings.settings.mainScrollableElementSelector | the main scrolling element}
*
* @throws {@link Errors.LisnUsageError | LisnUsageError}
* If the scrollable is invalid.
*/
readonly fetchCurrentScrollAction: (
scrollable?: Element,
) => Promise<ScrollAction | null>;
/**
* Cancels the ongoing scroll that's resulting from smooth scrolling
* triggered in the past. Does not interrupt or prevent further scrolling.
*
* @throws {@link Errors.LisnUsageError | LisnUsageError}
* If the scrollable is invalid.
*
* @param [options.immediate] If true, then it will not use
* {@link waitForMeasureTime} or
* {@link Utils.waitForMutateTime | waitForMutateTime}.
* Warning: this will likely result in forced layout.
*/
readonly stopUserScrolling: (options?: {
scrollable?: ScrollTarget;
immediate?: boolean;
}) => Promise<void>;
/**
* Returns the element that holds the main page content. By default it's
* `document.body` but is overridden by
* {@link Settings.settings.mainScrollableElementSelector}.
*
* It will wait for the element to be available if not already.
*/
static fetchMainContentElement(): Promise<HTMLElement> {
return fetchMainContentElement();
}
/**
* Returns the scrollable element that holds the wrapper around the main page
* content. By default it's `document.scrollable` (unless `document.body` is
* actually scrollable, in which case it will be used) but it will be
* different if {@link Settings.settings.mainScrollableElementSelector} is set.
*
* It will wait for the element to be available if not already.
*/
static fetchMainScrollableElement(): Promise<HTMLElement> {
return fetchMainScrollableElement();
}
/**
* Creates a new instance of ScrollWatcher with the given
* {@link ScrollWatcherConfig}. It does not save it for future reuse.
*/
static create(config?: ScrollWatcherConfig) {
return new ScrollWatcher(getConfig(config), CONSTRUCTOR_KEY);
}
/**
* Returns an existing instance of ScrollWatcher with the given
* {@link ScrollWatcherConfig}, or creates a new one.
*
* **NOTE:** It saves it for future reuse, so don't use this for temporary
* short-lived watchers.
*/
static reuse(config?: ScrollWatcherConfig) {
const myConfig = getConfig(config);
const configStrKey = objToStrKey(myConfig);
let instance = instances.get(configStrKey);
if (!instance) {
instance = new ScrollWatcher(myConfig, CONSTRUCTOR_KEY);
instances.set(configStrKey, instance);
}
return instance;
}
private constructor(
config: ScrollWatcherConfigInternal,
key: typeof CONSTRUCTOR_KEY,
) {
if (key !== CONSTRUCTOR_KEY) {
throw MH.illegalConstructorError("ScrollWatcher.create");
}
const logger = debug
? new debug.Logger({ name: "ScrollWatcher", logAtCreation: config })
: null;
const allScrollData = MH.newWeakMap<Element, ScrollData>();
const activeListeners = MH.newWeakMap<
ScrollTarget,
{ _nRealtime: number }
>();
const allCallbacks = newXWeakMap<
Element,
Map<OnScrollHandler, CallbackEntry>
>(() => MH.newMap());
// ----------
const fetchCurrentScroll = async (
element: Element,
realtime = false,
isScrollEvent = false,
): Promise<ScrollData> => {
// The scroll data can change event without a scroll event, e.g. by the
// element changing size, so always get the latest here.
const previousEventData = allScrollData.get(element);
const latestData = await fetchScrollData(
element,
previousEventData,
realtime,
);
// If there hasn't been a scroll event, use the old scroll direction
if (!isScrollEvent && previousEventData) {
latestData.direction = previousEventData.direction;
}
return latestData;
};
// ----------
const createCallback = (
handler: OnScrollHandler,
options: OnScrollOptionsInternal,
trackType: TrackType,
): CallbackEntry => {
const element = options._element;
MH.remove(allCallbacks.get(element)?.get(handler)?._callback);
debug: logger?.debug5("Adding/updating handler", options);
const callback = wrapCallback(handler, options._debounceWindow);
callback.onRemove(() => {
deleteHandler(handler, options);
});
const entry = {
_callback: callback,
_trackType: trackType,
_options: options,
};
allCallbacks.sGet(element).set(handler, entry);
return entry;
};
// ----------
const setupOnScroll = async (
handler: OnScrollHandler,
userOptions: OnScrollOptions | undefined,
trackType: TrackType,
) => {
const options = await fetchOnScrollOptions(config, userOptions ?? {});
const element = options._element;
// Don't await for the scroll data before creating the callback so that
// setupOnScroll and removeOnScroll have the same "timing" and therefore
// calling onScroll and offScroll immediately without awaiting removes the
// callback.
const entry = createCallback(handler, options, trackType);
const callback = entry._callback;
const eventTarget = options._eventTarget;
const scrollData = await fetchCurrentScroll(
element,
options._debounceWindow === 0,
);
if (callback.isRemoved()) {
return;
}
entry._data = scrollData;
allScrollData.set(element, scrollData);
if (trackType === TRACK_FULL) {
await setupSizeTrack(entry);
}
let listenerOptions = activeListeners.get(eventTarget);
if (!listenerOptions) {
debug: logger?.debug4("Adding scroll listener", eventTarget);
listenerOptions = { _nRealtime: 0 };
activeListeners.set(eventTarget, listenerOptions);
// Don't debounce the scroll handler, only the callbacks.
addEventListenerTo(eventTarget, MC.S_SCROLL, scrollHandler);
}
if (options._debounceWindow === 0) {
listenerOptions._nRealtime++;
}
const directions = options._directions;
if (
!callback.isRemoved() &&
!userOptions?.skipInitial &&
directionMatches(directions, scrollData.direction)
) {
debug: logger?.debug5("Calling initially with", element, scrollData);
// Use a one-off callback that's not debounced for the initial call.
await invokeCallback(wrapCallback(handler), element, scrollData);
}
};
// ----------
const removeOnScroll = async (
handler: OnScrollHandler,
scrollable: ScrollTarget | undefined,
trackType: TrackType,
) => {
const options = await fetchOnScrollOptions(config, { scrollable });
const element = options._element;
const currEntry = allCallbacks.get(element)?.get(handler);
if (currEntry?._trackType === trackType) {
MH.remove(currEntry._callback);
if (handler === setScrollCssProps) {
// delete the properties
setScrollCssProps(element, null);
}
}
};
// ----------
const deleteHandler = (
handler: OnScrollHandler,
options: OnScrollOptionsInternal,
) => {
const element = options._element;
const eventTarget = options._eventTarget;
MH.deleteKey(allCallbacks.get(element), handler);
allCallbacks.prune(element);
const listenerOptions = activeListeners.get(eventTarget);
if (listenerOptions && options._debounceWindow === 0) {
listenerOptions._nRealtime--;
}
if (!allCallbacks.has(element)) {
debug: logger?.debug4(
"No more callbacks for scrollable; removing listener",
element,
);
MH.deleteKey(allScrollData, element);
removeEventListenerFrom(eventTarget, MC.S_SCROLL, scrollHandler);
MH.deleteKey(activeListeners, eventTarget);
// TODO: Should we unwrap children if previously WE wrapped them?
}
};
// ----------
const setupSizeTrack = async (entry: CallbackEntry) => {
const options = entry._options;
const element = options._element;
const scrollCallback = entry._callback;
debug: logger?.debug8("Setting up size tracking", element);
const doc = MH.getDoc();
const docScrollingElement = MH.getDocScrollingElement();
const resizeCallback = wrapCallback(async () => {
// Get the latest scroll data for the scrollable
// Currently, the resize callback is already delayed by a frame due to
// the SizeWatcher, so we don't need to treat this as realtime.
const latestData = await fetchCurrentScroll(element);
const thresholdsExceeded = hasExceededThreshold(
options,
latestData,
entry._data,
);
if (!thresholdsExceeded) {
debug: logger?.debug9(
"Threshold not exceeded",
options,
latestData,
entry._data,
);
} else if (!scrollCallback.isRemoved()) {
await invokeCallback(scrollCallback, element, latestData);
}
});
scrollCallback.onRemove(resizeCallback.remove);
// Don't use default instance as it has a high threshold.
const sizeWatcher = SizeWatcher.reuse();
const setupOnResize = (target?: SizeTarget) =>
sizeWatcher.onResize(resizeCallback, {
target,
[MC.S_DEBOUNCE_WINDOW]: options._debounceWindow,
// TODO maybe accepts resizeThreshold option
threshold: options._threshold,
});
if (element === docScrollingElement) {
// In case we're tracking the main document scroll, then we only need to
// observe the viewport size and the size of the documentElement (which is
// the content size).
setupOnResize(); // viewport size
setupOnResize(doc); // content size
return;
}
// ResizeObserver only detects changes in offset width/height which is
// the visible size of the scrolling element, and that is not affected by the
// size of its content.
// But we also need to detect changes in the scroll width/height which is
// the size of the content.
// We also need to keep track of elements being added to the scrollable element.
const observedElements = MH.newSet<Element>([element]);
// Observe the scrolling element
setupOnResize(element);
// And also its children (if possible, a single wrapper around them
const wrapper = await tryWrapContent(element, {
_classNames: [
MC.PREFIX_WRAPPER,
MC.PREFIX_WRAPPER_CONTENT,
PREFIX_WRAPPER,
],
});
if (wrapper) {
setupOnResize(wrapper);
observedElements.add(wrapper);
//
} else {
for (const child of MH.childrenOf(element)) {
setupOnResize(child);
observedElements.add(child);
}
}
// Watch for newly added elements
const domWatcher = DOMWatcher.create({
root: element,
// only direct children
subtree: false,
});
const onAddedCallback = wrapCallback((operation: MutationOperation) => {
const child = MH.currentTargetOf(operation);
// If we've just added the wrapper, it will be in DOMWatcher's queue,
// so check.
if (child !== wrapper) {
if (wrapper) {
// Move this child into the wrapper. If this results in change of size
// for wrapper, SizeWatcher will call us.
moveElement(child, { to: wrapper, ignoreMove: true });
} else {
// Track the size of this child.
// Don't skip initial, call the callback now
setupOnResize(child);
observedElements.add(child);
}
}
});
domWatcher.onMutation(onAddedCallback, { categories: [MC.S_ADDED] });
resizeCallback.onRemove(onAddedCallback.remove);
};
// ----------
const scrollHandler = async (event: Event) => {
// We cannot use event.currentTarget because scrollHandler is called inside
// a setTimeout so by that time, currentTarget is null or something else.
//
// However, target and currentTarget only differ when the event is in the
// bubbling or capturing phase. Because
//
// - the scroll event only bubbles when fired on document, and (it only
// bubbles up to window)
// - and we never attach the listener to the capturing phase
// - and we always use document instead of window to listen for scroll on
// document
//
// then event.target suffices.
const scrollable = MH.targetOf(event);
/* istanbul ignore next */
if (!scrollable || !(MH.isElement(scrollable) || MH.isDoc(scrollable))) {
return;
}
const element = await fetchScrollableElement(scrollable);
const realtime = (activeListeners.get(scrollable)?._nRealtime ?? 0) > 0;
const latestData = await fetchCurrentScroll(element, realtime, true);
allScrollData.set(element, latestData);
debug: logger?.debug9("Scroll event", element, latestData);
for (const entry of allCallbacks.get(element)?.values() || []) {
// Consider the direction since the last scroll event and not the
// direction based on the largest delta the last time the callback
// was called.
const options = entry._options;
const thresholdsExceeded = hasExceededThreshold(
options,
latestData,
entry._data,
);
if (!thresholdsExceeded) {
debug: logger?.debug9(
"Threshold not exceeded",
options,
latestData,
entry._data,
);
continue;
}
// If threshold has been exceeded, always update the latest data for
// this callback.
const prevData = entry._data;
entry._data = latestData;
if (!directionMatches(options._directions, latestData.direction)) {
debug: logger?.debug9(
"Direction does not match",
options,
latestData,
);
continue;
}
invokeCallback(entry._callback, element, latestData, prevData);
}
};
// ----------
this.fetchCurrentScroll = (scrollable?, realtime?) =>
fetchScrollableElement(scrollable).then((element) =>
fetchCurrentScroll(element, realtime),
);
// ----------
this.scroll = (direction, options) => {
if (!isValidScrollDirection(direction)) {
throw MH.usageError(`Unknown scroll direction: '${direction}'`);
}
const isVertical = direction === MC.S_UP || direction === MC.S_DOWN;
const sign = direction === MC.S_UP || direction === MC.S_LEFT ? -1 : 1;
let targetCoordinate: TargetCoordinate;
const amount = options?.amount ?? 100;
const asFractionOf = options?.asFractionOf;
if (asFractionOf === "visible") {
targetCoordinate = isVertical
? (el) =>
el[MC.S_SCROLL_TOP] +
(sign * amount * getClientHeightNow(el)) / 100
: (el) =>
el[MC.S_SCROLL_LEFT] +
(sign * amount * getClientWidthNow(el)) / 100;
//
} else if (asFractionOf === "content") {
targetCoordinate = isVertical
? (el) =>
el[MC.S_SCROLL_TOP] +
(sign * amount * el[MC.S_SCROLL_HEIGHT]) / 100
: (el) =>
el[MC.S_SCROLL_LEFT] +
(sign * amount * el[MC.S_SCROLL_WIDTH]) / 100;
//
} else if (asFractionOf !== undefined && asFractionOf !== "pixel") {
throw MH.usageError(
`Unknown 'asFractionOf' keyword: '${asFractionOf}'`,
);
//
} else {
targetCoordinate = isVertical
? (el) => el[MC.S_SCROLL_TOP] + sign * amount
: (el) => el[MC.S_SCROLL_LEFT] + sign * amount;
}
const target = isVertical
? { top: targetCoordinate }
: { left: targetCoordinate };
return this.scrollTo(target, options);
};
// ----------
this.scrollTo = async (to, options) =>
scrollTo(
to,
MH.merge(options, {
duration: options?.duration ?? config._scrollDuration, // default
scrollable: await fetchScrollableElement(options?.scrollable), // override
}),
);
// ----------
this.fetchCurrentScrollAction = (scrollable?) =>
fetchScrollableElement(scrollable).then((element) =>
getCurrentScrollAction(element),
);
// ----------
this.stopUserScrolling = async (options) => {
const element = await fetchScrollableElement(options?.scrollable);
const stopScroll = () =>
MH.elScrollTo(element, {
top: element[MC.S_SCROLL_TOP],
left: element[MC.S_SCROLL_LEFT],
});
if (options?.immediate) {
stopScroll();
} else {
waitForMeasureTime().then(stopScroll);
}
};
// ----------
this.trackScroll = (handler?, options?) => {
if (!handler) {
handler = setScrollCssProps;
}
return setupOnScroll(handler, options, TRACK_FULL);
};
// ----------
this.noTrackScroll = (handler?, scrollable?) => {
if (!handler) {
handler = setScrollCssProps;
}
removeOnScroll(handler, scrollable, TRACK_FULL); // no need to await
};
// ----------
this.onScroll = (handler, options?) =>
setupOnScroll(handler, options, TRACK_REGULAR);
// ----------
this.offScroll = (handler, scrollable?) => {
removeOnScroll(handler, scrollable, TRACK_REGULAR); // no need to await
};
}
}
/**
* @interface
*/
export type ScrollWatcherConfig = {
/**
* The default value for
* {@link OnScrollOptions.debounceWindow | debounceWindow} in calls to
* {@link ScrollWatcher.onScroll}.
*
* @defaultValue 75
*/
debounceWindow?: number;
/**
* The default value for
* {@link OnScrollOptions.threshold | threshold} in calls to
* {@link ScrollWatcher.onScroll}.
*
* @defaultValue 50
*/
scrollThreshold?: number;
/**
* The default value for
* {@link ScrollOptions.duration | duration} in calls to
* {@link ScrollWatcher.scroll} and {@link ScrollWatcher.scrollTo}.
*
* @defaultValue 1000
*/
scrollDuration?: number;
};
/**
* @interface
*/
export type OnScrollOptions = {
/**
* If it is not given, or is `null`, `window` or `document`, then it will
* track the scroll of the
* {@link Settings.settings.mainScrollableElementSelector | the main scrolling element}.
*
* Other values must be an `Element` and are taken literally.
*
* @defaultValue undefined
*/
scrollable?: ScrollTarget;
/**
* If non-0, the scroll handler will only be called when the scrollable's
* scroll offset in the observed direction has changed at least
* `scrollThreshold` pixels since the last time the handler was called.
*
* @defaultValue {@link ScrollWatcherConfig.scrollThreshold}
*/
threshold?: number;
/**
* Specifies a list of {@link ScrollDirection}s to listen for.
*
* It can be a comma-separated list of direction names or an array of such
* names.
*
* If not given, then it listens for scrolls in any direction, including
* {@link Types.NoDirection} and {@link Types.AmbiguousDirection}.
*
* The {@link Types.NoDirection} occurs when the callback is called initially
* (if `skipInitial` is not `true`) and there hasn't yet been a scroll
* observed on the scrollable _and_ it's `scrollTop`/`scrollLeft` are 0.
*
* The {@link Types.AmbiguousDirection} occurs when the user scrolls
* diagonally with close to equal deltas in both horizontal and vertical
* direction.
*
* **IMPORTANT:**
*
* The direction of a scroll event is always based on comparing `deltaX` and
* `deltaY` relative to the _last scroll event_ (within the `debounceWindow`,
* and not to the scroll data for the last time the callback was called (in
* case it was skipped because `threshold` was not exceeded or in case it was
* debounced by a larger window than the watcher).
*
* I.e. if you have both `threshold` and `directions` restricted, or if the
* callback has a larger debounce window than the watcher, it is possible for
* there to be a change in the relevant `scrollTop`/`scrollLeft` offset that
* exceeds the threshold, and for the callback to _not_ be called.
*
* For a callback to be called, both of these must be true:
* - the change in `scrollTop`/`scrollLeft`, _compared to the last time the
* callback was called_ must exceed the {@link threshold}
* - the effective scroll direction, _compared to the last scroll event_
* prior to the _watcher's_ debounce window must be one of the given
* {@link directions}.
*
* @defaultValue undefined
*/
directions?: CommaSeparatedStr<ScrollDirection> | ScrollDirection[];
/**
* Do not call the handler until there's a future scroll of the element.
*
* By default we call the handler (almost) immediately if there's been a
* scroll in one of the given directions, or if there has not been a scroll
* but directions includes {@link Types.NoDirection}, but you can disable
* this initial call here.
*
* @defaultValue false
*/
skipInitial?: boolean;
/**
* If non-0, the handler will be "debounced" so it's called at most
* `debounceWindow` milliseconds.
*
* **IMPORTANT:**
* If the debounce window is non-0 (default), then the callback is always
* delayed by at least an animation frame following a scroll event to allow
* for optimized `scrollTop`/`scrollLeft` measurements via
* {@link waitForMeasureTime}.
*
* If you set this is 0, this indicates that the callback should be
* "realtime" and will therefore skip {@link waitForMeasureTime}, which could
* lead to forced re-layouts, but you probably need this when doing
* scroll-based animations.
*
* @defaultValue {@link ScrollWatcherConfig.debounceWindow}
*/
debounceWindow?: number;
};
/**
* @interface
*/
export type ScrollOptions = ScrollToOptions & {
/**
* How much to scroll in the given direction.
*
* @defaultValue 100
*/
amount?: number;
/**
* If set to "pixel" (default), `amount` is taken as absolute pixels.
*
* If set to "visible", `amount` is taken as percent of the element's visible
* size in the scrolling direction (100 means full client width for
* horizontal or height for vertical scroll).
*
* If set to "content", `amount` is taken as percent of the element's full
* content size in the scrolling direction (100 means full scroll width for
* horizontal or height for vertical scroll).
*
* @defaultValue "pixel"
*/
asFractionOf?: "pixel" | "visible" | "content";
};
/**
* The handler is invoked with three arguments:
*
* - The element that has been resized.
* - The latest {@link ScrollData} for the element.
* - (since v1.3.0) The {@link ScrollData} for the element when the thresholds
* for this callback were last exceeded. If the callback is called for any
* scroll direction, then this will be the data when it was last invoked. Will
* be `undefined` the first time.
*/
export type OnScrollHandlerArgs = [Element, ScrollData, ScrollData | undefined];
export type OnScrollCallback = Callback<OnScrollHandlerArgs>;
export type OnScrollHandler =
| CallbackHandler<OnScrollHandlerArgs>
| OnScrollCallback;
export type ScrollData = {
clientWidth: number;
clientHeight: number;
scrollWidth: number;
scrollHeight: number;
scrollTop: number;
/**
* This is the `scrollTop` relative to the full `scrollHeight` minus the
* `clientHeight`, ranging from 0 to 1.
*/
scrollTopFraction: number;
scrollLeft: number;
/**
* This is the `scrollLeft` relative to the full `scrollWidth` minus the
* `clientWidth`, ranging from 0 to 1.
*/
scrollLeftFraction: number;
/**
* This is the direction of the last scroll action, i.e. _compared to the
* last scroll event_, not necessarily based on the deltas compared to the
* last time this callback was called.
*/
direction: ScrollDirection;
};
// ----------------------------------------
type ScrollWatcherConfigInternal = {
_debounceWindow: number;
_scrollThreshold: number;
_scrollDuration: number;
};
type OnScrollOptionsInternal = {
_element: Element;
_eventTarget: ScrollTarget;
_directions: ScrollDirection[] | null;
_threshold: number;
_debounceWindow: number;
};
type CallbackEntry = {
_callback: OnScrollCallback;
_trackType: TrackType;
_options: OnScrollOptionsInternal;
_data?: ScrollData;
};
type TrackType = typeof TRACK_REGULAR | typeof TRACK_FULL;
const CONSTRUCTOR_KEY: unique symbol = MC.SYMBOL() as typeof CONSTRUCTOR_KEY;
const instances = MH.newMap<string, ScrollWatcher>();
const PREFIX_WRAPPER = MH.prefixName("scroll-watcher-wrapper");
const getConfig = (
config: ScrollWatcherConfig | undefined,
): ScrollWatcherConfigInternal => {
config ??= {};
return {
_debounceWindow: toNonNegNum(config[MC.S_DEBOUNCE_WINDOW], 75),
// If threshold is 0, internally treat as 1 (pixel)
_scrollThreshold: toNonNegNum(config.scrollThreshold, 50) || 1,
_scrollDuration: toNonNegNum(config.scrollDuration, 1000),
};
};
const TRACK_REGULAR = 1; // only scroll events
const TRACK_FULL = 2; // scroll + resizing of content and/or wrapper
// --------------------
const fetchOnScrollOptions = async (
config: ScrollWatcherConfigInternal,
options: OnScrollOptions,
): Promise<OnScrollOptionsInternal> => {
const directions =
validateStrList("directions", options.directions, isValidScrollDirection) ||
null;
const element = await fetchScrollableElement(options.scrollable);
return {
_element: element,
_eventTarget: getEventTarget(element),
_directions: directions,
// If threshold is 0, internally treat as 1 (pixel)
_threshold: toNonNegNum(options.threshold, config._scrollThreshold) || 1,
_debounceWindow: options[MC.S_DEBOUNCE_WINDOW] ?? config._debounceWindow,
};
};
const directionMatches = (
userDirections: ScrollDirection[] | null,
latestDirection: ScrollDirection,
) => !userDirections || MH.includes(userDirections, latestDirection);
const hasExceededThreshold = (
options: OnScrollOptionsInternal,
latestData: ScrollData,
lastThresholdData: ScrollData | undefined,
): boolean => {
const directions = options._directions;
const threshold = options._threshold;
Iif (!lastThresholdData) {
/* istanbul ignore */
return false;
}
const topDiff = maxAbs(
latestData[MC.S_SCROLL_TOP] - lastThresholdData[MC.S_SCROLL_TOP],
latestData[MC.S_SCROLL_HEIGHT] - lastThresholdData[MC.S_SCROLL_HEIGHT],
latestData[MC.S_CLIENT_HEIGHT] - lastThresholdData[MC.S_CLIENT_HEIGHT],
);
const leftDiff = maxAbs(
latestData[MC.S_SCROLL_LEFT] - lastThresholdData[MC.S_SCROLL_LEFT],
latestData[MC.S_SCROLL_WIDTH] - lastThresholdData[MC.S_SCROLL_WIDTH],
latestData[MC.S_CLIENT_WIDTH] - lastThresholdData[MC.S_CLIENT_WIDTH],
);
// If the callback is only interested in up/down, then only check the
// scrollTop delta, and similarly for left/right.
let checkTop = false,
checkLeft = false;
if (
!directions ||
MH.includes(directions, MC.S_NONE) ||
MH.includes(directions, MC.S_AMBIGUOUS)
) {
checkTop = checkLeft = true;
} else {
if (
MH.includes(directions, MC.S_UP) ||
MH.includes(directions, MC.S_DOWN)
) {
checkTop = true;
}
if (
MH.includes(directions, MC.S_LEFT) ||
MH.includes(directions, MC.S_RIGHT)
) {
checkLeft = true;
}
}
return (
(checkTop && topDiff >= threshold) || (checkLeft && leftDiff >= threshold)
);
};
const fetchScrollData = async (
element: Element,
previousEventData: ScrollData | undefined,
realtime: boolean,
): Promise<ScrollData> => {
if (!realtime) {
await waitForMeasureTime();
}
const scrollTop = MH.ceil(element[MC.S_SCROLL_TOP]);
const scrollLeft = MH.ceil(element[MC.S_SCROLL_LEFT]);
const scrollWidth = element[MC.S_SCROLL_WIDTH];
const scrollHeight = element[MC.S_SCROLL_HEIGHT];
const clientWidth = getClientWidthNow(element);
const clientHeight = getClientHeightNow(element);
const scrollTopFraction =
MH.round(scrollTop) / (scrollHeight - clientHeight || MC.INFINITY);
const scrollLeftFraction =
MH.round(scrollLeft) / (scrollWidth - clientWidth || MC.INFINITY);
const prevScrollTop = previousEventData?.scrollTop ?? 0;
const prevScrollLeft = previousEventData?.scrollLeft ?? 0;
const direction = getMaxDeltaDirection(
scrollLeft - prevScrollLeft,
scrollTop - prevScrollTop,
);
return {
direction,
[MC.S_CLIENT_WIDTH]: clientWidth,
[MC.S_CLIENT_HEIGHT]: clientHeight,
[MC.S_SCROLL_WIDTH]: scrollWidth,
[MC.S_SCROLL_HEIGHT]: scrollHeight,
[MC.S_SCROLL_TOP]: scrollTop,
[MC.S_SCROLL_TOP_FRACTION]: scrollTopFraction,
[MC.S_SCROLL_LEFT]: scrollLeft,
[MC.S_SCROLL_LEFT_FRACTION]: scrollLeftFraction,
};
};
const setScrollCssProps = (
element: Element,
scrollData: Partial<ScrollData> | undefined | null,
) => {
let prefix = "";
if (element === tryGetMainScrollableElement()) {
// Set the CSS vars on the root element
element = MH.getDocElement();
prefix = "page-";
}
scrollData ??= {};
const props = {
[MC.S_SCROLL_TOP]: scrollData[MC.S_SCROLL_TOP],
[MC.S_SCROLL_TOP_FRACTION]: scrollData[MC.S_SCROLL_TOP_FRACTION],
[MC.S_SCROLL_LEFT]: scrollData[MC.S_SCROLL_LEFT],
[MC.S_SCROLL_LEFT_FRACTION]: scrollData[MC.S_SCROLL_LEFT_FRACTION],
[MC.S_SCROLL_WIDTH]: scrollData[MC.S_SCROLL_WIDTH],
[MC.S_SCROLL_HEIGHT]: scrollData[MC.S_SCROLL_HEIGHT],
};
setNumericStyleJsVars(element, props, { _prefix: prefix });
};
const getEventTarget = (element: Element): ScrollTarget => {
if (element === MH.getDocScrollingElement()) {
return MH.getDoc();
}
return element;
};
const invokeCallback = (
callback: OnScrollCallback,
element: Element,
scrollData: ScrollData,
lastScrollData?: ScrollData,
) =>
callback
.invoke(
element,
MH.copyObject(scrollData),
lastScrollData, // no need to copy that one as it's not used again
)
.catch(logError);
|