Incorrect error object serialization

[junajan]

Hi, we are using this package through discordjs package and in some occasions (during high memory load) we can see this error in our logs:

Error: Unhandled 'error' event emitted, received [object Object]
    at WebSocketShard.emit (/app/node_modules/@vladfrangu/async_event_emitter/dist/index.cjs:276:19)
    at WebSocketShard.onError (/app/node_modules/@discordjs/ws/dist/index.js:1070:10)
    at connection.onerror (/app/node_modules/@discordjs/ws/dist/index.js:683:12)
    at callListener (/app/node_modules/ws/lib/event-target.js:290:14)
    at WebSocket.onError (/app/node_modules/ws/lib/event-target.js:230:9)
    at WebSocket.emit (node:events:519:28)
    at emitErrorAndClose (/app/node_modules/ws/lib/websocket.js:1041:13)
    at process.processTicksAndRejections (node:internal/process/task_queues:82:21)

On file and line @vladfrangu/async_event_emitter/dist/index.cjs:276:19 there is this code:

const err = new Error(`Unhandled 'error' event emitted, received ${stringifiedError}`);

Which is part of this class method:

  emit(eventName, ...args) {
    let doError = eventName === "error";
    const events = this._events;
    if (events !== void 0) {
      doError = doError && "error" in events;
    } else if (!doError) {
      return false;
    }
    if (doError) {
      let er;
      if (args.length > 0) {
        er = args[0];
      }
      if (er instanceof Error) {
        try {
          const capture = {};
          Error.captureStackTrace(capture, _AsyncEventEmitter.prototype.emit);
          Object.defineProperty(er, "stack", {
            value: enhanceStackTrace.call(this, er, capture),
            configurable: true
          });
        } catch {
        }
        throw er;
      }
      const stringifiedError = String(er);
      const err = new Error(`Unhandled 'error' event emitted, received ${stringifiedError}`); // <-- log message gets created here
      err.context = er;
      throw err;
    }
    const handlers = events[eventName];
    if (handlers === void 0) {
      return false;
    }
    if (typeof handlers === "function") {
      const result = handlers.apply(this, args);
      if (result !== void 0 && result !== null) {
        handleMaybeAsync(this, result);
      }
    } else {
      const len = handlers.length;
      const listeners = arrayClone(handlers);
      for (let i = 0; i < len; ++i) {
        const result = listeners[i].apply(this, args);
        if (result !== void 0 && result !== null) {
          handleMaybeAsync(this, result);
        }
      }
    }
    return true;
  }

It looks like in cases when er variable is an object it gets incorrectly stringified into [object Object] which hides original error.
Maybe something like JSON.stringify(er) would be more suitable?

[vladfrangu]

Unless NodeJS changed how they emit this, I am not keen on drifting from their output, be it as useless as [object Object] 😅