SJE is a custom Streamlit component, built to evaluate arbitrary Javascript expressions and return the result. It can become useful in doing certain functionalities which are simple things in JavaScript, but unavailable or difficult to do in Streamlit. Examples include cookie management, writing to clipboard, getting device width (e.g. to check if we are on a mobile device), getting browser language, sharing something through Android's share feature, knowing user agent, etc. See MDN docs for more information about Web APIs.

pip3 install streamlit_js_eval

st.write(f"Screen width is {streamlit_js_eval(js_expressions='screen.width', key = 'SCR')}")

key is an arbitrary but unique string, required by Streamlit components API for each call to streamlit_js_eval.

Some more common functionalities are already implemented as Python functions. Examples include:

# Returns user's location after asking for permission when the user clicks the generated link with the given text
location = get_geolocation()
# The URL parts of the page
location_json = get_page_location()

See streamlit_js_eval/__init__.py for more functions. Check a demo in example.py or see it live.

• It seems calling SJE from inside a branch in Streamlit code does not work (e.g. in a loop, if-else block, ...)