enable-threads.js

// NOTE: This file creates a service worker that cross-origin-isolates the page (read more here: https://web.dev/coop-coep/) which allows us to use wasm threads.
// Normally you would set the COOP and COEP headers on the server to do this, but Github Pages doesn't allow this, so this is a hack to do that.

/* Edited version of: coi-serviceworker v0.1.6 - Guido Zuidhof, licensed under MIT */
// From here: https://github.com/gzuidhof/coi-serviceworker
if(typeof window === 'undefined') {
 self.addEventListener("install", () => self.skipWaiting());
 self.addEventListener("activate", e => e.waitUntil(self.clients.claim()));

 async function handleFetch(request) {
 if(request.cache === "only-if-cached" && request.mode !== "same-origin") {
 return;
 }
 
 if(request.mode === "no-cors") { // We need to set `credentials` to "omit" for no-cors requests, per this comment: https://bugs.chromium.org/p/chromium/issues/detail?id=1309901#c7
 request = new Request(request.url, {
 cache: request.cache,
 credentials: "omit",
 headers: request.headers,
 integrity: request.integrity,
 destination: request.destination,
 keepalive: request.keepalive,
 method: request.method,
 mode: request.mode,
 redirect: request.redirect,
 referrer: request.referrer,
 referrerPolicy: request.referrerPolicy,
 signal: request.signal,
 });
 }
 
 let r = await fetch(request).catch(e => console.error(e));
 
 if(r.status === 0) {
 return r;
 }

 const headers = new Headers(r.headers);
 headers.set("Cross-Origin-Embedder-Policy", "credentialless"); // or: require-corp
 headers.set("Cross-Origin-Opener-Policy", "same-origin");
 
 return new Response(r.body, { status: r.status, statusText: r.statusText, headers });
 }

 self.addEventListener("fetch", function(e) {
 e.respondWith(handleFetch(e.request)); // respondWith must be executed synchonously (but can be passed a Promise)
 });
 
} else {
 (async function() {
 if(window.crossOriginIsolated !== false) return;

 let registration = await navigator.serviceWorker.register(window.document.currentScript.src).catch(e => console.error("COOP/COEP Service Worker failed to register:", e));
 if(registration) {
 console.log("COOP/COEP Service Worker registered", registration.scope);

 registration.addEventListener("updatefound", () => {
 console.log("Reloading page to make use of updated COOP/COEP Service Worker.");
 window.location.reload();
 });

 // If the registration is active, but it's not controlling the page
 if(registration.active && !navigator.serviceWorker.controller) {
 console.log("Reloading page to make use of COOP/COEP Service Worker.");
 window.location.reload();
 }
 }
 })();
}

// Code to deregister:
// let registrations = await navigator.serviceWorker.getRegistrations();
// for(let registration of registrations) {
// await registration.unregister();
// }