feat(theme): create more generic ThemedComponent util from ThemedImage

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

@@ -6,44 +6,21 @@
  */
 
 import React from 'react';
-import clsx from 'clsx';
-import useIsBrowser from '@docusaurus/useIsBrowser';
-import {useColorMode} from '@docusaurus/theme-common';
+import {ThemedComponent} from '@docusaurus/theme-common';
 import type {Props} from '@theme/ThemedImage';
 
-import styles from './styles.module.css';
-
 export default function ThemedImage(props: Props): JSX.Element {
-  const isBrowser = useIsBrowser();
-  const {colorMode} = useColorMode();
-  const {sources, className, alt, ...propsRest} = props;
-
-  type SourceName = keyof Props['sources'];
-
-  const clientThemes: SourceName[] =
-    colorMode === 'dark' ? ['dark'] : ['light'];
-
-  const renderedSourceNames: SourceName[] = isBrowser
-    ? clientThemes
-    : // We need to render both images on the server to avoid flash
-      // See https://github.com/facebook/docusaurus/pull/3730
-      ['light', 'dark'];
-
+  const {sources, className: parentClassName, alt, ...propsRest} = props;
   return (
-    <>
-      {renderedSourceNames.map((sourceName) => (
+    <ThemedComponent className={parentClassName}>
+      {({theme, className}) => (
         <img
-          key={sourceName}
-          src={sources[sourceName]}
+          src={sources[theme]}
           alt={alt}
-          className={clsx(
-            styles.themedImage,
-            styles[`themedImage--${sourceName}`],
-            className,
-          )}
+          className={className}
           {...propsRest}
         />
-      ))}
-    </>
+      )}
+    </ThemedComponent>
   );
 }

packages/docusaurus-theme-common/src/components/ThemedComponent/index.tsx

@@ -0,0 +1,77 @@
+/**
+ * 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 from 'react';
+import clsx from 'clsx';
+import useIsBrowser from '@docusaurus/useIsBrowser';
+import {useColorMode} from '../../contexts/colorMode';
+
+import styles from './styles.module.css';
+
+const AllThemes = ['light', 'dark'] as const;
+
+type Theme = (typeof AllThemes)[number];
+
+type RenderFn = ({
+  theme,
+  className,
+}: {
+  theme: Theme;
+  className: string;
+}) => React.ReactNode;
+
+type Props = {
+  children: RenderFn;
+  className?: string;
+};
+
+/**
+ * Generic component to render anything themed in light/dark
+ * Note: it's preferable to use CSS for theming because this component
+ * will need to render all the variants during SSR to avoid a theme flash.
+ *
+ * Use this only when CSS customizations are not convenient or impossible.
+ * For example, rendering themed images or SVGs...
+ *
+ * @param className applied to all the variants
+ * @param children function to render a theme variant
+ * @constructor
+ */
+export default function ThemedComponent({
+  className,
+  children,
+}: Props): JSX.Element {
+  const isBrowser = useIsBrowser();
+  const {colorMode} = useColorMode();
+
+  function getThemesToRender(): Theme[] {
+    if (isBrowser) {
+      return colorMode === 'dark' ? ['dark'] : ['light'];
+    }
+    // We need to render both components on the server / hydration to avoid:
+    // - a flash of wrong theme before hydration
+    // - React hydration mismatches
+    // See https://github.com/facebook/docusaurus/pull/3730
+    return ['light', 'dark'];
+  }
+
+  return (
+    <>
+      {getThemesToRender().map((theme) => {
+        const themedElement = children({
+          theme,
+          className: clsx(
+            className,
+            styles.themedComponent,
+            styles[`themedComponent--${theme}`],
+          ),
+        });
+        return <React.Fragment key={theme}>{themedElement}</React.Fragment>;
+      })}
+    </>
+  );
+}

packages/docusaurus-theme-common/src/components/ThemedComponent/styles.module.css

@@ -0,0 +1,18 @@
+/**
+ * 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.
+ */
+
+.themedComponent {
+  display: none;
+}
+
+[data-theme='light'] .themedComponent--light {
+  display: initial;
+}
+
+[data-theme='dark'] .themedComponent--dark {
+  display: initial;
+}

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

@@ -24,6 +24,8 @@ export {
   type ColorModeConfig,
 } from './utils/useThemeConfig';
 
+export {default as ThemedComponent} from './components/ThemedComponent';
+
 export {
   createStorageSlot,
   useStorageSlot,