Recreating D3 example failed

🐛 Bug

I tried to recreate an example for this D3 network graph in PyScript (minimal example here) then came across this error:

Uncaught TypeError: jsargs is not iterable (cannot read property undefined)
    at Proxy.apply (pyproxy.gen.ts:1145:19)
    at Dispatch.call (d3-dispatch.js:58:18)
    at step (d3-force.js:228:13)
    at timerFlush (d3-timer.js:49:15)
    at wake (d3-timer.js:58:5)

To Reproduce

See https://github.com/Cheukting/Cheukting.github.io/blob/master/assets/html/min-network-d3.html

Expected behavior

See https://d3-graph-gallery.com/graph/network_basic.html

[rth]

Thanks for investigating @leriomaggio and @hoodmane for fixing it in #3101!

[leriomaggio]

Ok so I played with it a little bit and here is what I found.

1. Re error: the error message is indeed a bit different but the essence is the same.

Expanding a bit about this (with the help of Browser inspector) in d3-dispatch.js (around lines 51-59)

51 call: function(type, that) {
         [...]
57     for (t = this._[type], i = 0, n = t.length; i < n; ++i)
58         t[i].value.apply(that, args);
59  },

L58 gets evaluated because this (the Dispatch) looks like:

this:  Dispatch
    _: 
        end: Array(1)
            0: {name: '', value: Proxy}
            length: 1

args will later be the jargs in question for PyProxy that is indeed undefined as none of the previous lines in call (from d3-dispatch.js) where evaluated.

Therefore, from the Pyodide side, these situations could be potentially accounted for by checking whether jargs is undefined or not and so call the PyObject accordingly.

I don’t know whether that makes any sense, tbh (disclaimer 😅 ), but I think the issue here is perhaps a bit more philosophical (re specific example, see below)

1. As for the specific example: I sensed the error could’ve been related to Proxy conversion - that is perhaps not the right thing to do here.

TLDR; I replaced create_proxy with create_once_callable for the ticked PyFunction and it works! This function is meant to be called once (on("end"..) in fact) Therefore I thought that a quick to consume PyProxy object is what was more appropriate… and it worked 🎉

More specifically on the issue: I looked carefully at what happens on the call stack when it generates the error.

• With Porxy, d3-dispatch evaluates immediately pyproxy-gen-ts (L1145) that raises the exception as the object in this is a Proxy (not being available yet from the promise? 🤔 )

• With Once Callable, this contains directly the wrapper function ready to be invoked by pyodide-asm (L14) which is indeed already the callable we need there 😃

I hope this helps in shading some light on the issue at hand?