An easy-to-use platform for EEG experimentation in the classroom
maybe a solution
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src/renderer/utils/webworker/webworker.js
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src/renderer/utils/webworker/webworker.js
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/**
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* Pyodide Web Worker — ES module worker following the pattern from
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* https://gitlab.com/castedo/pyodide-worker-example
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* Pyodide Web Worker — local node_modules implementation.
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*
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* Loading strategy
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* ----------------
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* 1. `import { loadPyodide } from "pyodide"` — Vite resolves this to
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* node_modules/pyodide/pyodide.mjs and serves it from /@fs/… in dev mode,
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* completely bypassing any publicDir transform issues.
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*
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* 2. `indexURL: '/pyodide/'` — tells pyodide where to find pyodide-lock.json
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* and binary package wheels (.whl). These are served from publicDir:
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* src/renderer/utils/webworker/src/pyodide/
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* which is populated by:
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* • InstallPyodide.mjs (copies pyodide-lock.json + runtime from npm)
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* • InstallMNE.mjs (downloads binary wheels from Pyodide CDN)
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*
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* 3. Binary packages (numpy / scipy / matplotlib / pandas) — loaded via
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* pyodide.loadPackage(), resolved from local /pyodide/ files.
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* Use Vite's `?url` suffix on 'pyodide/pyodide.mjs' to get the resolved file URL
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* at build/dev time (/@fs/... in dev, an asset URL in prod), then dynamically
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* import from that URL. This bypasses Vite's SPA fallback and lets pyodide.mjs
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* resolve all sibling assets (pyodide.asm.wasm, pyodide-lock.json, etc.) via
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* import.meta.url — no CDN required.
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*
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* 4. MNE + pure-Python deps — installed via micropip from pre-downloaded
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* wheels in /packages/, listed in /packages/manifest.json.
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* Populated by InstallMNE.mjs Part 2 (PyPI).
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* Production builds use the files copied to publicDir by InstallPyodide.mjs.
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*/
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import { loadPyodide } from 'pyodide';
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/**
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* Derive the renderer root URL from the worker's own location.
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*
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* Dev (Vite HTTP server): self.location.href is an http:// URL — the root is
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* just the origin, so root-relative paths work as normal.
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*
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* Production (Electron file://): Vite bundles workers into assets/, so the
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* renderer root is one directory above the worker file.
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*/
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function getRendererBaseUrl() {
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const loc = self.location.href;
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if (loc.startsWith('http')) {
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return new URL('/', loc).href;
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}
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// file:// — go up from assets/webworker-[hash].js to the renderer root
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return new URL('../', loc).href;
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}
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async function initPyodide() {
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const base = getRendererBaseUrl();
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// indexURL tells pyodide where to load pyodide-lock.json and binary wheels.
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// Resolved from the renderer root so it works under both HTTP (dev) and
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// file:// (Electron production).
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const pyodide = await loadPyodide({ indexURL: new URL('pyodide/', base).href });
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// Load binary packages from locally served .whl files.
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await pyodide.loadPackage(['numpy', 'scipy', 'matplotlib', 'pandas']);
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// ?url tells Vite to resolve the path and return a URL string rather than bundling
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// the module. In dev mode this is a /@fs/ URL (bypasses SPA fallback); in prod it
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// is an asset URL. We then dynamically import from that URL so pyodide.mjs can
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// resolve all its sibling assets (pyodide.asm.wasm, etc.) via import.meta.url.
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import pyodideMjsUrl from 'pyodide/pyodide.mjs?url';
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// Install MNE and its pure-Python deps from pre-downloaded wheels.
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let manifest = {};
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try {
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const res = await fetch(new URL('packages/manifest.json', base).href);
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if (res.ok) {
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manifest = await res.json();
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} else {
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console.warn('[pyodide worker] manifest.json not found — MNE unavailable');
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}
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} catch (err) {
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console.warn('[pyodide worker] Could not fetch manifest.json:', err);
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}
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const wheelUrls = Object.values(manifest).map(
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(entry) => new URL(`packages/${entry.filename}`, base).href
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);
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if (wheelUrls.length > 0) {
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await pyodide.loadPackage('micropip');
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const micropip = pyodide.pyimport('micropip');
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await micropip.install(wheelUrls);
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} else {
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console.warn('[pyodide worker] No MNE wheels in manifest — skipping micropip install');
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}
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return pyodide;
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}
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// Start loading immediately so it is ready when the first message arrives.
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const pyodideReadyPromise = initPyodide();
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const pyodideReadyPromise = (async () => {
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const { loadPyodide } = await import(/* @vite-ignore */ pyodideMjsUrl);
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return loadPyodide();
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})();
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self.onmessage = async (event) => {
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// Propagate init failures back to the main thread rather than hanging silently.