Catch WebSocket JS exceptions in library_websocket.js

[johnwason]

Version of emscripten/emsdk:
Please include the output emcc -v here

I am using the latest Pyodide master version that appears to be using Emscripten version 3.1.52

I am receiving errors such as the following console message when using WebSockets:

pyodide.asm.js:9 Uncaught DOMException: Failed to execute 'close' on 'WebSocket': The close code must be either 1000, or between 3000 and 4999. 0 is neither.
    at _emscripten_websocket_close (http://localhost:8000/robotraconteur_pyodide/pyodide/pyodide.asm.js:9:519374)
    at wasm://wasm/04206a8e:wasm-function[8899]:0xaba21d
    at invoke_vi (http://localhost:8000/robotraconteur_pyodide/pyodide/pyodide.asm.js:9:1214419)
    at wasm://wasm/04206a8e:wasm-function[8893]:0xab775b
    at socket.onclose (http://localhost:8000/robotraconteur_pyodide/pyodide/pyodide.asm.js:9:516980)

WebSocket is already in CLOSING or CLOSED state.

And then a long WASM stack trace that I can't seem to copy out of the log for some reason.

It appears that the library_websocket.js functions are not catching JS exceptions generated by WebSocket functions, and are instead letting the JS exceptions pass back into WASM where they can't be caught. This is resulting in my entire application crashing. While my software clearly has some problems with how it is using WebSockets, if the error return was being handled correctly it would be able to recover. They JS exceptions should be caught, and an error code gracefully returned.

This is something I can work on in the next few weeks.