fix: polyfill Map.prototype.getOrInsertComputed to stop PDF.js render crash

Fixes #662

src/js/utils/map-upsert-polyfill.ts

@@ -0,0 +1,47 @@
+type MapPrototypeWithUpsert = typeof Map.prototype & {
+  getOrInsert?: (key: unknown, value: unknown) => unknown;
+  getOrInsertComputed?: (
+    key: unknown,
+    callback: (key: unknown) => unknown
+  ) => unknown;
+};
+
+const mapPrototype = Map.prototype as MapPrototypeWithUpsert;
+const mapHas = Map.prototype.has;
+const mapGet = Map.prototype.get;
+const mapSet = Map.prototype.set;
+
+if (typeof mapPrototype.getOrInsert !== 'function') {
+  Object.defineProperty(mapPrototype, 'getOrInsert', {
+    configurable: true,
+    writable: true,
+    value: function getOrInsert(key: unknown, value: unknown) {
+      if (mapHas.call(this, key)) return mapGet.call(this, key);
+      mapSet.call(this, key, value);
+      return value;
+    },
+  });
+}
+
+if (typeof mapPrototype.getOrInsertComputed !== 'function') {
+  Object.defineProperty(mapPrototype, 'getOrInsertComputed', {
+    configurable: true,
+    writable: true,
+    value: function getOrInsertComputed(
+      key: unknown,
+      callback: (key: unknown) => unknown
+    ) {
+      const hasKey = mapHas.call(this, key);
+      if (typeof callback !== 'function') {
+        throw new TypeError('callback must be a function');
+      }
+      if (hasKey) return mapGet.call(this, key);
+
+      const value = callback(key);
+      mapSet.call(this, key, value);
+      return value;
+    },
+  });
+}
+
+export {};