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* Adapts focus styles based on the user's active input modality (i.e., how
* they are interacting with the UI right now).
*
* Focus styles are only relevant when using the keyboard to interact with the
* page. If we only show the focus ring when relevant, we can avoid user
* confusion without compromising accessibility.
*
* The script uses two heuristics to determine whether the keyboard is being used:
*
* 1. a keydown event occurred immediately before a focus event;
* 2. a focus event happened on an element which requires keyboard interaction (e.g., a text field);
*
* This software or document includes material copied from or derived from https://github.com/WICG/focus-visible.
* Copyright © 2018 W3C® (MIT, ERCIM, Keio, Beihang).
* W3C Software Notice and License: https://www.w3.org/Consortium/Legal/2015/copyright-software-and-document
*
* @noflow
*/
import { canUseDOM } from 'fbjs/lib/ExecutionEnvironment';
const focusVisibleAttributeName = 'data-focusvisible-polyfill';
const rule = `:focus:not([${focusVisibleAttributeName}]){outline: none;}`;
const modality = (insertRule) => {
insertRule(rule);
if (!canUseDOM) {
return;
}
let hadKeyboardEvent = true;
let hadFocusVisibleRecently = false;
let hadFocusVisibleRecentlyTimeout = null;
const inputTypesWhitelist = {
text: true,
search: true,
url: true,
tel: true,
email: true,
password: true,
number: true,
date: true,
month: true,
week: true,
time: true,
datetime: true,
'datetime-local': true
};
/**
* Helper function for legacy browsers and iframes which sometimes focus
* elements like document, body, and non-interactive SVG.
*/
function isValidFocusTarget(el) {
if (
el &&
el !== document &&
el.nodeName !== 'HTML' &&
el.nodeName !== 'BODY' &&
'classList' in el &&
'contains' in el.classList
) {
return true;
}
return false;
}
/**
* Computes whether the given element should automatically trigger the
* `focus-visible` attribute being added, i.e. whether it should always match
* `:focus-visible` when focused.
*/
function focusTriggersKeyboardModality(el) {
const type = el.type;
const tagName = el.tagName;
const isReadOnly = el.readOnly;
Iif (tagName === 'INPUT' && inputTypesWhitelist[type] && !isReadOnly) {
return true;
}
Iif (tagName === 'TEXTAREA' && !isReadOnly) {
return true;
}
Iif (el.isContentEditable) {
return true;
}
return false;
}
/**
* Add the `focus-visible` attribute to the given element if it was not added by
* the author.
*/
function addFocusVisibleAttribute(el) {
if (el.hasAttribute(focusVisibleAttributeName)) {
return;
}
el.setAttribute(focusVisibleAttributeName, true);
}
/**
* Remove the `focus-visible` attribute from the given element if it was not
* originally added by the author.
*/
function removeFocusVisibleAttribute(el) {
el.removeAttribute(focusVisibleAttributeName);
}
/**
* Remove the `focus-visible` attribute from all elements in the document.
*/
function removeAllFocusVisibleAttributes() {
const list = document.querySelectorAll(`[${focusVisibleAttributeName}]`);
for (let i = 0; i < list.length; i += 1) {
removeFocusVisibleAttribute(list[i]);
}
}
/**
* Treat `keydown` as a signal that the user is in keyboard modality.
* Apply `focus-visible` to any current active element and keep track
* of our keyboard modality state with `hadKeyboardEvent`.
*/
function onKeyDown(e) {
if (e.key !== 'Tab' && (e.metaKey || e.altKey || e.ctrlKey || e.shiftKey)) {
return;
}
Iif (isValidFocusTarget(document.activeElement)) {
addFocusVisibleAttribute(document.activeElement);
}
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.
* It also avoids the situation where a user presses on an element within a
* previously keyboard-focused element (i.e., `e.target` is not the previously
* focused element, but one of its descendants) and we need to remove the
* focus ring because a `blur` event doesn't occur.
*/
function onPointerDown(e) {
if (hadKeyboardEvent === true) {
removeAllFocusVisibleAttributes();
}
hadKeyboardEvent = false;
}
/**
* On `focus`, add the `focus-visible` attribute to the target if:
* - the target received focus as a result of keyboard navigation, or
* - the event target is an element that will likely require interaction
* via the keyboard (e.g. a text box)
*/
function onFocus(e) {
// Prevent IE from focusing the document or HTML element.
if (!isValidFocusTarget(e.target)) {
return;
}
if (hadKeyboardEvent || focusTriggersKeyboardModality(e.target)) {
addFocusVisibleAttribute(e.target);
}
}
/**
* On `blur`, remove the `focus-visible` attribute from the target.
*/
function onBlur(e) {
if (!isValidFocusTarget(e.target)) {
return;
}
Eif (e.target.hasAttribute(focusVisibleAttributeName)) {
// 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(function () {
hadFocusVisibleRecently = false;
window.clearTimeout(hadFocusVisibleRecentlyTimeout);
}, 100);
removeFocusVisibleAttribute(e.target);
}
}
/**
* If the user changes tabs, keep track of whether or not the previously
* focused element had the focus-visible attribute.
*/
function onVisibilityChange(e) {
if (document.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 attribute when the user switches back to the tab.
if (hadFocusVisibleRecently) {
hadKeyboardEvent = true;
}
addInitialPointerMoveListeners();
}
}
/**
* Add a group of listeners to detect usage of any pointing devices.
* These listeners will be added when the polyfill first loads, and anytime
* the window is blurred, so that they are active when the window regains
* focus.
*/
function addInitialPointerMoveListeners() {
document.addEventListener('mousemove', onInitialPointerMove);
document.addEventListener('mousedown', onInitialPointerMove);
document.addEventListener('mouseup', onInitialPointerMove);
document.addEventListener('pointermove', onInitialPointerMove);
document.addEventListener('pointerdown', onInitialPointerMove);
document.addEventListener('pointerup', onInitialPointerMove);
document.addEventListener('touchmove', onInitialPointerMove);
document.addEventListener('touchstart', onInitialPointerMove);
document.addEventListener('touchend', onInitialPointerMove);
}
function removeInitialPointerMoveListeners() {
document.removeEventListener('mousemove', onInitialPointerMove);
document.removeEventListener('mousedown', onInitialPointerMove);
document.removeEventListener('mouseup', onInitialPointerMove);
document.removeEventListener('pointermove', onInitialPointerMove);
document.removeEventListener('pointerdown', onInitialPointerMove);
document.removeEventListener('pointerup', onInitialPointerMove);
document.removeEventListener('touchmove', onInitialPointerMove);
document.removeEventListener('touchstart', onInitialPointerMove);
document.removeEventListener('touchend', onInitialPointerMove);
}
/**
* When the polfyill first loads, assume the user is in keyboard modality.
* If any event is received from a pointing device (e.g. mouse, pointer,
* touch), turn off keyboard modality.
* This accounts for situations where focus enters the page from the URL bar.
*/
function onInitialPointerMove(e) {
// Work around a Safari quirk that fires a mousemove on <html> whenever the
// window blurs, even if you're tabbing out of the page. ¯\_(ツ)_/¯
Iif (e.target.nodeName === 'HTML') {
return;
}
hadKeyboardEvent = false;
removeInitialPointerMoveListeners();
}
document.addEventListener('keydown', onKeyDown, true);
document.addEventListener('mousedown', onPointerDown, true);
document.addEventListener('pointerdown', onPointerDown, true);
document.addEventListener('touchstart', onPointerDown, true);
document.addEventListener('focus', onFocus, true);
document.addEventListener('blur', onBlur, true);
document.addEventListener('visibilitychange', onVisibilityChange, true);
addInitialPointerMoveListeners();
};
export default modality;
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