app.py

from h2o_wave import main, app, Q, ui


@app('/')
async def serve(q: Q):
    # Run this part only once, when the browser first connects.
    if not q.client.initialized:
        # Create a navigation card.
        q.page['nav'] = ui.nav_card(
            box='1 1 2 -1',
            # Use default value initially.
            value='#menu/spam',
            title='H2O Wave',
            items=[
                ui.nav_group('Menu', items=[
                    ui.nav_item(name='#menu/spam', label='Spam'),
                    ui.nav_item(name='#menu/ham', label='Ham'),
                    ui.nav_item(name='#menu/eggs', label='Eggs'),
                    ui.nav_item(name='#menu/toast', label='Toast'),
                ])
            ]
        )
        q.client.initialized = True

    # Check if a link is clicked or active in URL.
    if q.args['#'] is not None:
        # Update just the value.
        q.page['nav'].value = f'#{q.args["#"]}'

    await q.page.save()