Handle context menu format bold and italic

example/src/App.tsx

@@ -15,6 +15,18 @@ import {PlatformInfo} from './PlatformInfo';
 // We don't need this workaround in New Expensify App since Reanimated is imported before Live Markdown.
 console.log(Animated);
 
+function handleFormatSelection(selectedText: string, formatCommand: string) {
+  if (formatCommand === 'formatBold') {
+    return `*${selectedText}*`;
+  }
+
+  if (formatCommand === 'formatItalic') {
+    return `_${selectedText}_`;
+  }
+
+  return selectedText;
+}
+
 export default function App() {
   const [value, setValue] = React.useState(TEST_CONST.EXAMPLE_CONTENT);
   const [textColorState, setTextColorState] = React.useState(false);
@@ -48,6 +60,7 @@ export default function App() {
       <PlatformInfo />
       <MarkdownTextInput
         multiline
+        formatSelection={handleFormatSelection}
         autoCapitalize="none"
         value={value}
         onChangeText={setValue}

src/MarkdownTextInput.tsx

@@ -53,6 +53,7 @@ function unregisterParser(parserId: number) {
 
 interface MarkdownTextInputProps extends TextInputProps, InlineImagesInputProps {
   markdownStyle?: PartialMarkdownStyle;
+  formatSelection?: (selectedText: string, formatCommand: string) => string;
   parser: (value: string) => MarkdownRange[];
 }
 

src/MarkdownTextInput.web.tsx

@@ -30,6 +30,7 @@ const useClientEffect = typeof window === 'undefined' ? useEffect : useLayoutEff
 interface MarkdownTextInputProps extends TextInputProps, InlineImagesInputProps {
   markdownStyle?: MarkdownStyle;
   parser: (text: string) => MarkdownRange[];
+  formatSelection?: (selectedText: string, formatCommand: string) => string;
   onClick?: (e: MouseEvent<HTMLDivElement>) => void;
   dir?: string;
   disabled?: boolean;
@@ -85,6 +86,7 @@ const MarkdownTextInput = React.forwardRef<MarkdownTextInput, MarkdownTextInputP
       multiline = false,
       markdownStyle,
       parser,
+      formatSelection,
       onBlur,
       onChange,
       onChangeText,
@@ -236,6 +238,29 @@ const MarkdownTextInput = React.forwardRef<MarkdownTextInput, MarkdownTextInputP
       [parser, parseText, processedMarkdownStyle],
     );
 
+    const handleFormatSelection = useCallback(
+      (target: MarkdownTextInputElement, parsedText: string, cursorPosition: number, formatCommand: string): ParseTextResult => {
+        if (!contentSelection.current || contentSelection.current.end - contentSelection.current.start < 1) {
+          throw new Error('[react-native-live-markdown] invalid selection');
+        }
+
+        const selectedText = parsedText.slice(contentSelection.current.start, contentSelection.current.end);
+        const formattedText = formatSelection?.(selectedText, formatCommand) ?? selectedText;
+
+        if (selectedText === formattedText) {
+          return parseText(parser, target, parsedText, processedMarkdownStyle, cursorPosition);
+        }
+
+        const prefix = parsedText.slice(0, contentSelection.current.start);
+        const suffix = parsedText.slice(contentSelection.current.end);
+        const diffLength = formattedText.length - selectedText.length;
+        const text = `${prefix}${formattedText}${suffix}`;
+
+        return parseText(parser, target, text, processedMarkdownStyle, cursorPosition + diffLength, true);
+      },
+      [parser, parseText, formatSelection, processedMarkdownStyle],
+    );
+
     // Placeholder text color logic
     const updateTextColor = useCallback(
       (node: HTMLDivElement, text: string) => {
@@ -361,6 +386,11 @@ const MarkdownTextInput = React.forwardRef<MarkdownTextInput, MarkdownTextInputP
           case 'historyRedo':
             newInputUpdate = redo(divRef.current);
             break;
+          case 'formatBold':
+          case 'formatItalic':
+          case 'formatUnderline':
+            newInputUpdate = handleFormatSelection(divRef.current, parsedText, newCursorPosition, inputType);
+            break;
           default:
             newInputUpdate = parseText(parser, divRef.current, parsedText, processedMarkdownStyle, newCursorPosition, true, !inputType, inputType === 'pasteText');
         }
@@ -414,7 +444,21 @@ const MarkdownTextInput = React.forwardRef<MarkdownTextInput, MarkdownTextInputP
 
         handleContentSizeChange();
       },
-      [parser, updateTextColor, updateSelection, onChange, onChangeText, handleContentSizeChange, undo, redo, parseText, processedMarkdownStyle, setEventProps, maxLength],
+      [
+        parser,
+        updateTextColor,
+        updateSelection,
+        onChange,
+        onChangeText,
+        handleContentSizeChange,
+        undo,
+        redo,
+        handleFormatSelection,
+        parseText,
+        processedMarkdownStyle,
+        setEventProps,
+        maxLength,
+      ],
     );
 
     const insertText = useCallback(