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useIsFocusVisible.js
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Mon, Jan 27, 07:28

useIsFocusVisible.js
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// based on https://github.com/WICG/focus-visible/blob/v4.1.5/src/focus-visible.js
import * as React from 'react';
let hadKeyboardEvent = true;
let hadFocusVisibleRecently = false;
let hadFocusVisibleRecentlyTimeout;
const inputTypesWhitelist = {
text: true,
search: true,
url: true,
tel: true,
email: true,
password: true,
number: true,
date: true,
month: true,
week: true,
time: true,
datetime: true,
'datetime-local': true
};
/**
* Computes whether the given element should automatically trigger the
* `focus-visible` class being added, i.e. whether it should always match
* `:focus-visible` when focused.
* @param {Element} node
* @returns {boolean}
*/
function focusTriggersKeyboardModality(node) {
const {
type,
tagName
} = node;
if (tagName === 'INPUT' && inputTypesWhitelist[type] && !node.readOnly) {
return true;
}
if (tagName === 'TEXTAREA' && !node.readOnly) {
return true;
}
if (node.isContentEditable) {
return true;
}
return false;
}
/**
* Keep track of our keyboard modality state with `hadKeyboardEvent`.
* If the most recent user interaction was via the keyboard;
* and the key press did not include a meta, alt/option, or control key;
* then the modality is keyboard. Otherwise, the modality is not keyboard.
* @param {KeyboardEvent} event
*/
function handleKeyDown(event) {
if (event.metaKey || event.altKey || event.ctrlKey) {
return;
}
hadKeyboardEvent = true;
}
/**
* If at any point a user clicks with a pointing device, ensure that we change
* the modality away from keyboard.
* This avoids the situation where a user presses a key on an already focused
* element, and then clicks on a different element, focusing it with a
* pointing device, while we still think we're in keyboard modality.
*/
function handlePointerDown() {
hadKeyboardEvent = false;
}
function handleVisibilityChange() {
if (this.visibilityState === 'hidden') {
// If the tab becomes active again, the browser will handle calling focus
// on the element (Safari actually calls it twice).
// If this tab change caused a blur on an element with focus-visible,
// re-apply the class when the user switches back to the tab.
if (hadFocusVisibleRecently) {
hadKeyboardEvent = true;
}
}
}
function prepare(doc) {
doc.addEventListener('keydown', handleKeyDown, true);
doc.addEventListener('mousedown', handlePointerDown, true);
doc.addEventListener('pointerdown', handlePointerDown, true);
doc.addEventListener('touchstart', handlePointerDown, true);
doc.addEventListener('visibilitychange', handleVisibilityChange, true);
}
export function teardown(doc) {
doc.removeEventListener('keydown', handleKeyDown, true);
doc.removeEventListener('mousedown', handlePointerDown, true);
doc.removeEventListener('pointerdown', handlePointerDown, true);
doc.removeEventListener('touchstart', handlePointerDown, true);
doc.removeEventListener('visibilitychange', handleVisibilityChange, true);
}
function isFocusVisible(event) {
const {
target
} = event;
try {
return target.matches(':focus-visible');
} catch (error) {
// Browsers not implementing :focus-visible will throw a SyntaxError.
// We use our own heuristic for those browsers.
// Rethrow might be better if it's not the expected error but do we really
// want to crash if focus-visible malfunctioned?
}
// No need for validFocusTarget check. The user does that by attaching it to
// focusable events only.
return hadKeyboardEvent || focusTriggersKeyboardModality(target);
}
export default function useIsFocusVisible() {
const ref = React.useCallback(node => {
if (node != null) {
prepare(node.ownerDocument);
}
}, []);
const isFocusVisibleRef = React.useRef(false);
/**
* Should be called if a blur event is fired
*/
function handleBlurVisible() {
// checking against potential state variable does not suffice if we focus and blur synchronously.
// React wouldn't have time to trigger a re-render so `focusVisible` would be stale.
// Ideally we would adjust `isFocusVisible(event)` to look at `relatedTarget` for blur events.
// This doesn't work in IE11 due to https://github.com/facebook/react/issues/3751
// TODO: check again if React releases their internal changes to focus event handling (https://github.com/facebook/react/pull/19186).
if (isFocusVisibleRef.current) {
// To detect a tab/window switch, we look for a blur event followed
// rapidly by a visibility change.
// If we don't see a visibility change within 100ms, it's probably a
// regular focus change.
hadFocusVisibleRecently = true;
window.clearTimeout(hadFocusVisibleRecentlyTimeout);
hadFocusVisibleRecentlyTimeout = window.setTimeout(() => {
hadFocusVisibleRecently = false;
}, 100);
isFocusVisibleRef.current = false;
return true;
}
return false;
}
/**
* Should be called if a blur event is fired
*/
function handleFocusVisible(event) {
if (isFocusVisible(event)) {
isFocusVisibleRef.current = true;
return true;
}
return false;
}
return {
isFocusVisibleRef,
onFocus: handleFocusVisible,
onBlur: handleBlurVisible,
ref
};
}

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