WASM support #3311

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1. CoolCat467 commented on Aug 4, 2025

   

   CoolCat467

   on Aug 4, 2025

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   On https://pyodide.org/en/stable/console.html (had to hack the script to use v0.28.0 instead of 0.28.1)

   >>> import micropip
   >>> await micropip.install("trio")
   >>> import trio
   Traceback (most recent call last):
     File "<console>", line 1, in <module>
     File "/lib/python3.13/site-packages/trio/__init__.py", line 22, in <module>
       from ._core import TASK_STATUS_IGNORED as TASK_STATUS_IGNORED  # isort: split
       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
     File "/lib/python3.13/site-packages/trio/_core/__init__.py", line 21, in <module>
       from ._local import RunVar, RunVarToken
     File "/lib/python3.13/site-packages/trio/_core/_local.py", line 9, in <module>
       from . import _run
     File "/lib/python3.13/site-packages/trio/_core/_run.py", line 3004, in <module>
       raise NotImplementedError("unsupported platform")
   NotImplementedError: unsupported platform

   So kind of success so far, can install at least, but needs work of course
2. davidbrochart commented on Aug 4, 2025

   

   davidbrochart

   on Aug 4, 2025

   Last edited by davidbrochart

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   Maybe you just want to run a trio event loop on its own as a first step, but it's worth mentioning that pyodide integrates asyncio into the JavaScript event loop here. That allows e.g. JavaScript to await a Python task.
3. A5rocks commented on Aug 7, 2025

   

   A5rocks

   on Aug 7, 2025

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   I would expect we don't need any special support in pyodide because of trio.lowlevel.wait_task_rescheduled (for Python awaiting JS) and the other way around is probably simple to do with plain JS promises.

   ---

   So kind of success so far, can install at least, but needs work of course

   Yeah, I think that means we don't have an IO manager for it.
4. A5rocks commented on May 23, 2026

   

   A5rocks

   on May 23, 2026

   Last edited by A5rocks

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   I made a prototype version. See https://github.com/A5rocks/trio/tree/wasm-trio, you can run it via uv run -m build && uv run -m http.server, then open http://localhost:8000 and try something like this in the console:

   pyodide.runPython(`
   import trio
   
   async def main():
     await trio.sleep(1)
     return 5
   
   print(trio.run(main))`)

   Unfortunately, there doesn't seem to be a way to suspend execution. This makes this entirely impractical, since it means you won't be able to reschedule from e.g. promises. It's possible to work around this, but that would mean no return value from trio.run (note: it's synchronous!).

   The best alternate implementation probably involves spitting a signal at the program like in https://pyodide.org/en/stable/usage/keyboard-interrupts.html but that's pyodide specific. This is all just supposed to be whimsical so I don't really think it's worth tying ourselves to a particular implementation for practical results.

   👍React with 👍3Reacted by CoolCat467, John Litborn and Abduaziz