Polyfill PDF.js Map upsert inside worker

static/pdf-worker-wrapper.mjs

@@ -0,0 +1,17 @@
+if (!Map.prototype.getOrInsertComputed) {
+  Map.prototype.getOrInsertComputed = function(key, callback) {
+    if (this.has(key)) return this.get(key);
+    const value = callback(key);
+    this.set(key, value);
+    return value;
+  };
+}
+
+const pendingMessages = [];
+const bufferMessage = event => pendingMessages.push(event);
+self.addEventListener("message", bufferMessage);
+
+import("./vendor/pdf.worker.min.mjs").then(() => {
+  self.removeEventListener("message", bufferMessage);
+  for (const event of pendingMessages) self.dispatchEvent(new MessageEvent("message", { data: event.data }));
+});

static/reader.js

@@ -1,5 +1,5 @@
 const PDFJS_URL = "/static/vendor/pdf.min.mjs";
-const PDFJS_WORKER_URL = "/static/vendor/pdf.worker.min.mjs";
+const PDFJS_WORKER_URL = "/static/pdf-worker-wrapper.mjs";
 const EPUB_URL = "/static/vendor/epub.min.js";
 const MARKED_URL = "/static/vendor/marked.min.js";
 const PURIFY_URL = "/static/vendor/purify.min.js";