Pass errors through postMessage

client/src/index.ts

@@ -39,7 +39,20 @@ class GanacheWorkerProvider implements Eip1193Provider {
     public request(request: Request): Promise<any> {
         return new Promise((res, rej) => {
             const channel = new MessageChannel();
-            channel.port1.onmessage = (evt) => res(evt.data);
+            channel.port1.onmessage = (evt) => {
+                const data: unknown = evt.data;
+                if (!data || typeof data !== "object") {
+                    return rej();
+                }
+
+                if ("result" in data) {
+                    return res(data.result);
+                } else if ("error" in data) {
+                    return rej(data.error);
+                } else {
+                    return rej();
+                }
+            };
             channel.port1.onmessageerror = (evt) => rej(evt.data);
             this.worker.postMessage(request, [channel.port2]);
         });

client/src/worker_chain.ts

@@ -17,9 +17,15 @@ function onMessage(ganache: EthereumProvider, evt: MessageEvent): void {
         // message data conforms to the JSON RPC spec.
         // eslint-disable-next-line @typescript-eslint/no-unsafe-argument
         .request(evt.data)
-        .then((response) => reply.postMessage(response))
+        .then((result) => reply.postMessage({ result }))
         .catch((error) => {
             console.error("Uncaught (in ganache worker thread)", error);
+            reply.postMessage({
+                error: {
+                    message: String(error),
+                    code: -32000,
+                },
+            });
         });
 }