Update README.md

README.md

@@ -162,11 +162,30 @@ As _stlite_ runs on the web browser environment ([Pyodide](https://pyodide.org/)
 - `st.progress()` does not show the progress bar during the script execution, but shows only the last state after the execution finishes.
 - `time.sleep()` is no-op. This is a problem at Pyodide runtime. See https://github.com/pyodide/pyodide/issues/2354
 - `st.experimental_data_editor` does not work as it relies on PyArrow, but it doesn't work on Pyodide. Track this issue on https://github.com/whitphx/stlite/issues/509.
+- For URL access, `urllib` or `requests` don't work on Pyodide/stlite, so we have to use alternative methods provided by Pyodide, such as [`pyodide.http.pyfetch()`](https://pyodide.org/en/stable/usage/api/python-api/http.html#pyodide.http.pyfetch) or [`pyodide.http.open_url()`](https://pyodide.org/en/stable/usage/api/python-api/http.html#pyodide.http.open_url). See https://pyodide.org/en/stable/usage/faq.html#how-can-i-load-external-files-in-pyodide for the details. For `pyodide.http.pyfetch()`, see also the following section about top-level await.
 - The C extension packages that are not built for Pyodide cannot be installed. See https://pyodide.org/en/stable/usage/faq.html#micropip-can-t-find-a-pure-python-wheel for the details.
 
 Other problems are tracked at GitHub Issues: https://github.com/whitphx/stlite/issues
 If you find a new problem, please report it.
 
+## Top-level await
+
+Unlike the original Streamlit, stlite supports top-level await due to the differences in their execution models. Streamlit runs in a standard Python environment, allowing the use of `asyncio.run()` when an async function needs to be executed within a script. In contrast, stlite runs in a web browser, operating in an environment where the only event loop is always in a running state. This makes it impossible to use `asyncio.run()` within a script, necessitating the support for top-level await.
+
+Top-level await can be useful in various situations, such as when accessing external resources. In the Pyodide environment, widely-used URL access methods in Python, like `requests`, are not available. However, Pyodide provides [`pyodide.http.pyfetch()`](https://pyodide.org/en/stable/usage/api/python-api/http.html#pyodide.http.pyfetch) as an alternative for accessing external resources. Since this method is async, top-level await becomes handy for utilizing `pyodide.http.pyfetch()`.
+
+Here's a sample code snippet demonstrating the usage of top-level await with `pyodide.http.pyfetch()`:
+
+```python
+import pyodide.http
+
+url = "your_url_here"
+response = await pyodide.http.pyfetch(url)
+data_in_bytes = await response.bytes()
+```
+
+This code snippet shows how to use top-level await to fetch data from an external resource using `pyodide.http.pyfetch()` and retrieve the response data in bytes format.
+
 ## Resources
 
 - [📖 Streamlit meets WebAssembly - stlite, by whitphx](https://www.whitphx.info/posts/20221104-streamlit-wasm-stlite/): A blog post covering from some technical surveys to the usages of the online editor _stlite sharing_, self-hosting apps, and the desktop app bundler.