Fix #5855.

src/element/textWysiwyg.test.tsx

@@ -933,7 +933,7 @@ describe("textWysiwyg", () => {
 
       await new Promise((cb) => setTimeout(cb, 0));
       editor.blur();
-      expect(rectangle.width).toBe(110);
+      expect(rectangle.width).toBe(100);
       expect(rectangle.height).toBe(210);
       const textElement = h.elements[1] as ExcalidrawTextElement;
       expect(textElement.text).toBe(wrappedText);

src/element/textWysiwyg.tsx

@@ -290,14 +290,21 @@ export const textWysiwyg = ({
         fontSize: app.state.currentItemFontSize,
         fontFamily: app.state.currentItemFontFamily,
       });
-      const wrappedText = container
-        ? wrapText(data, font, getMaxContainerWidth(container))
-        : data;
 
-      const dimensions = measureText(wrappedText, font);
-      editable.style.height = `${dimensions.height}px`;
-
-      onChange(wrappedText);
+      if (data) {
+        const text = editable.value;
+        const start = Math.min(editable.selectionStart, editable.selectionEnd);
+        const end = Math.max(editable.selectionStart, editable.selectionEnd);
+        const newText = `${text.substring(0, start)}${data}${text.substring(
+          end,
+        )}`;
+        const wrappedText = container
+          ? wrapText(newText, font, getMaxContainerWidth(container!))
+          : newText;
+        const dimensions = measureText(wrappedText, font);
+        editable.style.height = `${dimensions.height}px`;
+        onChange(newText);
+      }
     };
     editable.oninput = () => {
       const updatedTextElement = Scene.getScene(element)?.getElement(