gristlabs_grist-core/app/client/lib/FocusLayer.ts

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/**
* FocusLayer addresses the issue of where focus goes "by default". In most of Grist operation,
* the focus is on the special Clipboard element to support typing into cells, and copy-pasting.
* When a modal is open, the focus is on the modal.
*
* When the focus moves to some specific element such as a textbox or a dropdown menu, the
* FocusLayerManager will watch for this element to lose focus or to get disposed, and will
* restore focus to the default element.
*/
import {arrayRemove} from 'app/common/gutil';
import {RefCountMap} from 'app/common/RefCountMap';
import {Disposable, dom} from 'grainjs';
/**
* The default focus is organized into layers. A layer determines when focus should move to the
* default element, and what that element should be. Only the top (most recently created) layer is
* active at any given time.
*/
export interface FocusLayerOptions {
// The default element that should have focus while this layer is active.
defaultFocusElem: HTMLElement;
// When true for an element, that element may hold focus even while this layer is active.
allowFocus: (elem: Element) => boolean;
// Called when the defaultFocusElem gets focused.
onDefaultFocus?: () => void;
// Called when the defaultFocusElem gets blurred.
onDefaultBlur?: () => void;
}
// Use RefCountMap to have a reference-counted instance of the global FocusLayerManager. It will
// be active as long as at least one FocusLayer is active (i.e. not disposed).
const _focusLayerManager = new RefCountMap<null, FocusLayerManager>({
create: (key) => FocusLayerManager.create(null),
dispose: (key, value) => value.dispose(),
gracePeriodMs: 10,
});
/**
* The FocusLayerManager implements the functionality, using the top (most recently created) layer
* to determine when and to what to move focus.
*/
class FocusLayerManager extends Disposable {
private _timeoutId: ReturnType<typeof setTimeout> | null = null;
private _focusLayers: FocusLayer[] = [];
constructor() {
super();
const grabFocus = this.grabFocus.bind(this);
this.autoDispose(dom.onElem(window, 'focus', grabFocus));
this.grabFocus();
// The following block of code deals with what happens when the window is in the background.
// When it is, focus and blur events are unreliable, and we'll watch explicitly for events which
// may cause a change in focus. These wouldn't happen normally for a background window, but do
// happen in Selenium Webdriver testing.
function setBackgroundCapture(onOff: boolean) {
const addRemove = onOff ? window.addEventListener : window.removeEventListener;
// Note the third argument useCapture=true, which lets us notice these events before other
// code that might call .stopPropagation on them.
addRemove.call(window, 'click', grabFocus, true);
addRemove.call(window, 'mousedown', grabFocus, true);
addRemove.call(window, 'keydown', grabFocus, true);
}
this.autoDispose(dom.onElem(window, 'blur', setBackgroundCapture.bind(null, true)));
this.autoDispose(dom.onElem(window, 'focus', setBackgroundCapture.bind(null, false)));
setBackgroundCapture(!document.hasFocus());
}
public addLayer(layer: FocusLayer) {
this._focusLayers.push(layer);
// Move the focus to the new layer. Not just grabFocus, because if the focus is on the previous
// layer's defaultFocusElem, the new layer might consider it "allowed" and never get the focus.
setTimeout(() => layer.defaultFocusElem.focus(), 0);
}
public removeLayer(layer: FocusLayer) {
arrayRemove(this._focusLayers, layer);
// Give the remaining layers a chance to check focus.
this.grabFocus();
}
public getCurrentLayer(): FocusLayer|undefined {
return this._focusLayers[this._focusLayers.length - 1];
}
/**
* Select the default focus element, or wait until the current element loses focus.
*/
public grabFocus() {
if (!this._timeoutId) {
this._timeoutId = setTimeout(() => this._doGrabFocus(), 0);
}
}
private _doGrabFocus() {
if (this.isDisposed()) { return; }
this._timeoutId = null;
const layer = this.getCurrentLayer();
if (!layer || document.activeElement === layer.defaultFocusElem) {
return;
}
// If the window doesn't have focus, don't rush to grab it, or we can interfere with focus
// outside the frame when embedded. We'll grab focus when setBackgroundCapture tells us to.
if (!document.hasFocus()) {
return;
}
if (document.activeElement && layer.allowFocus(document.activeElement)) {
watchElementForBlur(document.activeElement, () => this.grabFocus());
layer.onDefaultBlur?.();
} else {
layer.defaultFocusElem.focus();
layer.onDefaultFocus?.();
}
}
}
/**
* An individual FocusLayer determines where focus should default to while this layer is active.
*/
export class FocusLayer extends Disposable implements FocusLayerOptions {
// FocusLayer.grabFocus() allows triggering the focus check manually.
public static grabFocus() {
_focusLayerManager.get(null)?.grabFocus();
}
public defaultFocusElem: HTMLElement;
public allowFocus: (elem: Element) => boolean;
public onDefaultFocus?: () => void;
public onDefaultBlur?: () => void;
constructor(options: FocusLayerOptions) {
super();
this.defaultFocusElem = options.defaultFocusElem;
this.allowFocus = options.allowFocus;
this.onDefaultFocus = options.onDefaultFocus;
this.onDefaultBlur = options.onDefaultBlur;
const managerRefCount = this.autoDispose(_focusLayerManager.use(null));
const manager = managerRefCount.get();
manager.addLayer(this);
this.onDispose(() => manager.removeLayer(this));
this.autoDispose(dom.onElem(this.defaultFocusElem, 'blur', () => manager.grabFocus()));
}
}
/**
* Helper to watch a focused element to lose focus, at which point callback() will get called.
* Because elements getting removed from the DOM don't always trigger 'blur' event, this also
* uses MutationObserver to watch for the element to get removed from DOM.
*/
function watchElementForBlur(elem: Element, callback: () => void) {
const maybeDone = () => {
if (document.activeElement !== elem) {
lis.dispose();
observer.disconnect();
callback();
}
};
const lis = dom.onElem(elem, 'blur', maybeDone);
// Watch for the removal of elem by observing the childList of all its ancestors.
// (Just guessing that it is more efficient than watching document.body with {subtree: true}).
const observer = new MutationObserver(maybeDone);
let parent = elem.parentNode;
while (parent) {
observer.observe(parent, {childList: true});
parent = parent.parentNode;
}
}