Runs onload handler for browser navigations (backwards and forwards)

mesop/examples/__init__.py

@@ -8,6 +8,9 @@
   boilerplate_free_event_handlers as boilerplate_free_event_handlers,
 )
 from mesop.examples import box as box
+from mesop.examples import (
+  browser_navigation_on_load as browser_navigation_on_load,
+)
 from mesop.examples import buttons as buttons
 from mesop.examples import checkbox_and_radio as checkbox_and_radio
 from mesop.examples import composite as composite

mesop/examples/browser_navigation_on_load.py

@@ -0,0 +1,32 @@
+import mesop as me
+
+
+@me.stateclass
+class State:
+  page_1_onload_counter: int
+  page_2_onload_counter: int
+
+
+def page_1_on_load(e: me.LoadEvent):
+  me.state(State).page_1_onload_counter += 1
+
+
+@me.page(path="/browser_navigation_on_load/page1", on_load=page_1_on_load)
+def page1():
+  me.text("page1")
+  me.text(f"onload ran {me.state(State).page_1_onload_counter} times")
+  me.button("navigate", on_click=navigate)
+
+
+def navigate(e: me.ClickEvent):
+  me.navigate("/browser_navigation_on_load/page2")
+
+
+def page_2_on_load(e: me.LoadEvent):
+  me.state(State).page_2_onload_counter += 1
+
+
+@me.page(path="/browser_navigation_on_load/page2", on_load=page_2_on_load)
+def page2():
+  me.text("page2")
+  me.text(f"onload ran {me.state(State).page_2_onload_counter} times")

mesop/protos/ui.proto

@@ -24,7 +24,7 @@ message QueryParam {
     repeated string values = 2;
 }
 
-// Next ID: 19
+// Next ID: 20
 message UserEvent {
     optional States states = 1;
 
@@ -43,6 +43,7 @@ message UserEvent {
         double double_value = 7;
         int32 int_value = 8;
         NavigationEvent navigation = 6;
+        HotReloadEvent hot_reload = 19;
         ResizeEvent resize = 10;
         bytes bytes_value = 9;
         ChangePrefersColorScheme change_prefers_color_scheme = 14;
@@ -107,10 +108,14 @@ message DateRangePickerEvent {
   optional string end_date = 2;
 }
 
-// This is a user-triggered navigation (e.g. go back/forwards) or a hot reload event.
+// This is a user-triggered navigation (e.g. go back/forwards).
 message NavigationEvent{
 }
 
+// Fired when a hot reload is triggered.
+message HotReloadEvent {
+}
+
 // Fired whenever a user resizes the viewport/browser.
 message ResizeEvent {
 }

mesop/runtime/context.py

@@ -280,6 +280,7 @@ def run_event_handler(
   ) -> Generator[None, None, None]:
     if (
       event.HasField("navigation")
+      or event.HasField("hot_reload")
       or event.HasField("resize")
       or event.HasField("change_prefers_color_scheme")
     ):

mesop/server/server.py

@@ -193,9 +193,18 @@ def generate_data(ui_request: pb.UiRequest) -> Generator[str, None, None]:
           runtime().context().reset_previous_node()
         runtime().context().reset_current_node()
 
-        result = runtime().context().run_event_handler(ui_request.user_event)
         path = ui_request.path
         has_run_navigate_on_load = False
+
+        if ui_request.user_event.HasField("navigation"):
+          page_config = runtime().get_page_config(path=path)
+          if (
+            page_config and page_config.on_load and not has_run_navigate_on_load
+          ):
+            has_run_navigate_on_load = True
+            yield from run_page_load(path=path)
+
+        result = runtime().context().run_event_handler(ui_request.user_event)
         for _ in result:
           navigate_commands = [
             command
@@ -223,14 +232,7 @@ def generate_data(ui_request: pb.UiRequest) -> Generator[str, None, None]:
                 and not has_run_navigate_on_load
               ):
                 has_run_navigate_on_load = True
-                result = page_config.on_load(LoadEvent(path=path))
-                # on_load is a generator function then we need to iterate through
-                # the generator object.
-                if result:
-                  for _ in result:
-                    yield from render_loop(path=path, init_request=True)
-                    runtime().context().set_previous_node_from_current_node()
-                    runtime().context().reset_current_node()
+                yield from run_page_load(path=path)
 
           yield from render_loop(path=path)
           runtime().context().set_previous_node_from_current_node()
@@ -248,6 +250,18 @@ def generate_data(ui_request: pb.UiRequest) -> Generator[str, None, None]:
         error=pb.ServerError(exception=str(e), traceback=format_traceback())
       )
 
+  def run_page_load(*, path: str):
+    page_config = runtime().get_page_config(path=path)
+    assert page_config and page_config.on_load
+    result = page_config.on_load(LoadEvent(path=path))
+    # on_load is a generator function then we need to iterate through
+    # the generator object.
+    if result:
+      for _ in result:
+        yield from render_loop(path=path, init_request=True)
+        runtime().context().set_previous_node_from_current_node()
+        runtime().context().reset_current_node()
+
   @flask_app.route(UI_PATH, methods=["POST"])
   def ui_stream() -> Response:
     # Prevent CSRF by checking the request site matches the site

mesop/tests/e2e/browser_navigation_test.ts

@@ -0,0 +1,25 @@
+import {test, expect} from '@playwright/test';
+
+test('browser navigation - back and forward (triggers onload)', async ({
+  page,
+}) => {
+  await page.goto('/browser_navigation_on_load/page1');
+  await expect(page.getByText('page1')).toBeVisible();
+  await expect(page.getByText('onload ran 1 times')).toBeVisible();
+
+  // Trigger a navigation.
+  await page.getByRole('button', {name: 'navigate'}).click();
+
+  await expect(page.getByText('page2')).toBeVisible();
+  await expect(page.getByText('onload ran 1 times')).toBeVisible();
+
+  // Go back to page 1
+  await page.goBack();
+  await expect(page.getByText('page1')).toBeVisible();
+  await expect(page.getByText('onload ran 2 times')).toBeVisible();
+
+  // Go forward to page 2
+  await page.goForward();
+  await expect(page.getByText('page2')).toBeVisible();
+  await expect(page.getByText('onload ran 2 times')).toBeVisible();
+});

mesop/web/src/services/channel.ts

@@ -7,10 +7,10 @@ import {
   UserEvent,
   Component as ComponentProto,
   UiResponse,
-  NavigationEvent,
   ComponentConfig,
   Command,
   ChangePrefersColorScheme,
+  HotReloadEvent,
 } from 'mesop/mesop/protos/ui_jspb_proto_pb/mesop/protos/ui_pb';
 import {Logger} from '../dev_tools/services/logger';
 import {Title} from '@angular/platform-browser';
@@ -482,8 +482,7 @@ export class Channel {
     const request = new UiRequest();
     const userEvent = new UserEvent();
     userEvent.setStates(this.states);
-    const navigationEvent = new NavigationEvent();
-    userEvent.setNavigation(navigationEvent);
+    userEvent.setHotReload(new HotReloadEvent());
     userEvent.setViewportSize(getViewportSize());
     userEvent.setThemeSettings(this.themeService.getThemeSettings());
     userEvent.setQueryParamsList(getQueryParams());