Cannot understand ui.run_javascript()

[snoman88]

Question

I want to store the return value of ui.run_javascript() into a variable, but something strange happened while using ui.run_javascript().

First case:

from nicegui import ui
async def get_client_lang():
    return await ui.run_javascript('navigator.language')

async def notify_lang():
    ui.notify(await get_client_lang())


@ui.page('/')
async def index():
    ui.button('get lang', on_click=notify_lang)

ui.run()

That runs well.

Next case:

from nicegui import ui
async def get_client_lang():
    return await ui.run_javascript('navigator.language')

async def notify_lang():
    ui.notify(await get_client_lang())


@ui.page('/')
async def index():
    lang = await get_client_lang()
    ui.button('get lang', on_click=ui.notify(lang))


ui.run()

This case, lang = await get_client_lang() causes TimeoutError: JavaScript did not respond within 1.0 s.

Are there special cautions when using that function?
How can I store the return value of ui.run_javascript()?

[python-and-fiction]

you should wait client connected.

async def get_client_lang():
    return await ui.run_javascript('navigator.language')

async def notify_lang():
    ui.notify(await get_client_lang())


@ui.page('/')
async def index():
    await ui.context.client.connected()
    lang = await get_client_lang()
    ui.button('get lang', on_click=lambda :ui.notify(lang))

[snoman88]

I see.
javascript doesn't work until client connects.