feat(app): add is_web property

CHANGELOG.md

@@ -28,6 +28,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Added `min_color` and `max_color` to Sparklines constructor, which take precedence over CSS https://github.com/Textualize/textual/pull/5174
 - Added new demo `python -m textual`, not *quite* finished but better than the old one https://github.com/Textualize/textual/pull/5174
 - Added `Screen.can_view_partial` and `Widget.can_view_partial` https://github.com/Textualize/textual/pull/5174
+- Added `App.is_web` property to indicate if the app is running via a web browser https://github.com/Textualize/textual/pull/5128
 
 ### Fixed
 

src/textual/app.py

@@ -1002,6 +1002,11 @@ def is_inline(self) -> bool:
         """Is the app running in 'inline' mode?"""
         return False if self._driver is None else self._driver.is_inline
 
+    @property
+    def is_web(self) -> bool:
+        """Is the app running in 'web' mode via a browser?"""
+        return False if self._driver is None else self._driver.is_web
+
     @property
     def screen_stack(self) -> list[Screen[Any]]:
         """A snapshot of the current screen stack.

src/textual/driver.py

@@ -54,6 +54,11 @@ def is_inline(self) -> bool:
         """Is the driver 'inline' (not full-screen)?"""
         return False
 
+    @property
+    def is_web(self) -> bool:
+        """Is the driver 'web' (running via a browser)?"""
+        return False
+
     @property
     def can_suspend(self) -> bool:
         """Can this driver be suspended?"""

src/textual/drivers/web_driver.py

@@ -69,6 +69,10 @@ def __init__(
         """Maps delivery keys to file-like objects, used
         for delivering files to the browser."""
 
+    @property
+    def is_web(self) -> bool:
+        return True
+
     def write(self, data: str) -> None:
         """Write string data to the output device, which may be piped to
         the parent process (i.e. textual-web/textual-serve).