fix(theme-classic): fix SkipToContent without JS , refactor, make it …

…public theming API (#8204)

Co-authored-by: sebastienlorber <lorber.sebastien@gmail.com>

packages/docusaurus-theme-classic/src/getSwizzleConfig.ts

@@ -377,6 +377,14 @@ export default function getSwizzleConfig(): SwizzleConfig {
         description:
           'The search bar component of your site, appearing in the navbar.',
       },
+      SkipToContent: {
+        actions: {
+          eject: 'safe',
+          wrap: 'safe',
+        },
+        description:
+          'The component responsible for implementing the accessibility "skip to content" link (https://www.w3.org/TR/WCAG20-TECHS/G1.html)',
+      },
       'prism-include-languages': {
         actions: {
           eject: 'safe',

packages/docusaurus-theme-classic/src/theme/Layout/index.tsx

@@ -8,7 +8,11 @@
 import React from 'react';
 import clsx from 'clsx';
 import ErrorBoundary from '@docusaurus/ErrorBoundary';
-import {PageMetadata, ThemeClassNames} from '@docusaurus/theme-common';
+import {
+  PageMetadata,
+  SkipToContentFallbackId,
+  ThemeClassNames,
+} from '@docusaurus/theme-common';
 import {useKeyboardNavigation} from '@docusaurus/theme-common/internal';
 import SkipToContent from '@theme/SkipToContent';
 import AnnouncementBar from '@theme/AnnouncementBar';
@@ -42,6 +46,7 @@ export default function Layout(props: Props): JSX.Element {
       <Navbar />
 
       <div
+        id={SkipToContentFallbackId}
         className={clsx(
           ThemeClassNames.wrapper.main,
           styles.mainWrapper,

packages/docusaurus-theme-classic/src/theme/SkipToContent/index.tsx

@@ -6,26 +6,10 @@
  */
 
 import React from 'react';
-import Translate, {translate} from '@docusaurus/Translate';
-import {useSkipToContent} from '@docusaurus/theme-common/internal';
+import {SkipToContentLink} from '@docusaurus/theme-common';
 
 import styles from './styles.module.css';
 
 export default function SkipToContent(): JSX.Element {
-  const {containerRef, handleSkip} = useSkipToContent();
-  return (
-    <div
-      ref={containerRef}
-      role="region"
-      aria-label={translate({id: 'theme.common.skipToMainContent'})}>
-      {/* eslint-disable-next-line jsx-a11y/anchor-is-valid */}
-      <a href="#" className={styles.skipToContent} onClick={handleSkip}>
-        <Translate
-          id="theme.common.skipToMainContent"
-          description="The skip to content label used for accessibility, allowing to rapidly navigate to main content with keyboard tab/enter navigation">
-          Skip to main content
-        </Translate>
-      </a>
-    </div>
-  );
+  return <SkipToContentLink className={styles.skipToContent} />;
 }

packages/docusaurus-theme-common/src/index.ts

@@ -81,4 +81,9 @@ export {useDocsPreferredVersion} from './contexts/docsPreferredVersion';
 
 export {processAdmonitionProps} from './utils/admonitionUtils';
 
+export {
+  SkipToContentFallbackId,
+  SkipToContentLink,
+} from './utils/skipToContentUtils';
+
 export {ErrorBoundaryTryAgainButton} from './utils/errorBoundaryUtils';

packages/docusaurus-theme-common/src/internal.ts

@@ -117,6 +117,5 @@ export {
 export {useLockBodyScroll} from './hooks/useLockBodyScroll';
 export {useSearchPage} from './hooks/useSearchPage';
 export {useCodeWordWrap} from './hooks/useCodeWordWrap';
-export {useSkipToContent} from './hooks/useSkipToContent';
 export {getPrismCssVariables} from './utils/codeBlockUtils';
 export {useBackToTopButton} from './hooks/useBackToTopButton';

packages/docusaurus-theme-common/src/utils/skipToContentUtils.tsx

@@ -0,0 +1,103 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import React, {useCallback, useRef, type ComponentProps} from 'react';
+import {useHistory} from '@docusaurus/router';
+import {translate} from '@docusaurus/Translate';
+import {useLocationChange} from './useLocationChange';
+
+/**
+ * The id of the element that should become focused on a page
+ * that does not have a <main> html tag.
+ * Focusing the Docusaurus Layout children is a reasonable fallback.
+ */
+export const SkipToContentFallbackId = 'docusaurus_skipToContent_fallback';
+
+/**
+ * Returns the skip to content element to focus when the link is clicked.
+ */
+function getSkipToContentTarget(): HTMLElement | null {
+  return (
+    // Try to focus the <main> in priority
+    // Note: this will only work if JS is enabled
+    // See https://github.com/facebook/docusaurus/issues/6411#issuecomment-1284136069
+    document.querySelector('main:first-of-type') ??
+    // Then try to focus the fallback element (usually the Layout children)
+    document.getElementById(SkipToContentFallbackId)
+  );
+}
+
+function programmaticFocus(el: HTMLElement) {
+  el.setAttribute('tabindex', '-1');
+  el.focus();
+  el.removeAttribute('tabindex');
+}
+
+/** This hook wires the logic for a skip-to-content link. */
+function useSkipToContent(): {
+  /**
+   * The ref to the container. On page transition, the container will be focused
+   * so that keyboard navigators can instantly interact with the link and jump
+   * to content.
+   */
+  containerRef: React.RefObject<HTMLDivElement>;
+  /**
+   * Callback fired when the skip to content link has been clicked.
+   * It will programmatically focus the main content.
+   */
+  onClick: (e: React.MouseEvent<HTMLAnchorElement>) => void;
+} {
+  const containerRef = useRef<HTMLDivElement>(null);
+  const {action} = useHistory();
+
+  const onClick = useCallback((e: React.MouseEvent<HTMLAnchorElement>) => {
+    e.preventDefault();
+    const targetElement = getSkipToContentTarget();
+    if (targetElement) {
+      programmaticFocus(targetElement);
+    }
+  }, []);
+
+  // "Reset" focus when navigating.
+  // See https://github.com/facebook/docusaurus/pull/8204#issuecomment-1276547558
+  useLocationChange(({location}) => {
+    if (containerRef.current && !location.hash && action === 'PUSH') {
+      programmaticFocus(containerRef.current);
+    }
+  });
+
+  return {containerRef, onClick};
+}
+
+const DefaultSkipToContentLabel = translate({
+  id: 'theme.common.skipToMainContent',
+  description:
+    'The skip to content label used for accessibility, allowing to rapidly navigate to main content with keyboard tab/enter navigation',
+  message: 'Skip to main content',
+});
+
+type SkipToContentLinkProps = Omit<ComponentProps<'a'>, 'href' | 'onClick'>;
+
+export function SkipToContentLink(props: SkipToContentLinkProps): JSX.Element {
+  const linkLabel = props.children ?? DefaultSkipToContentLabel;
+  const {containerRef, onClick} = useSkipToContent();
+  return (
+    <div
+      ref={containerRef}
+      role="region"
+      aria-label={DefaultSkipToContentLabel}>
+      <a
+        {...props}
+        // Note this is a fallback href in case JS is disabled
+        // It has limitations, see https://github.com/facebook/docusaurus/issues/6411#issuecomment-1284136069
+        href={`#${SkipToContentFallbackId}`}
+        onClick={onClick}>
+        {linkLabel}
+      </a>
+    </div>
+  );
+}