mongodb/node-mongodb-native · error · MongoRuntimeError

An unexpected error type: ${typeof error}

Error message

An unexpected error type: ${typeof error}

What it means

Thrown inside `Server.decorateCommandError` when a command fails with a value that is not an object, is null, or has no `name` property (server.ts:456). The driver expects errors to be Error-like objects so it can decorate them with retry/label metadata; a primitive (string/number/boolean) or null error cannot be processed.

Source

Thrown at src/sdam/server.ts:457

        markServerUnknown(this, error);
      } else if (connection) {
        this.pool.clear({ serviceId: connection.serviceId });
      }
    }
  }

  /**
   * Ensure that error is properly decorated and internal state is updated before throwing
   * @internal
   */
  private decorateCommandError(
    connection: Connection,
    cmd: Document,
    options: CommandOptions | GetMoreOptions | undefined,
    error: unknown
  ): Error {
    if (typeof error !== 'object' || error == null || !('name' in error)) {
      throw new MongoRuntimeError('An unexpected error type: ' + typeof error);
    }

    if (error.name === 'AbortError' && 'cause' in error && error.cause instanceof MongoError) {
      error = error.cause;
    }

    if (!(error instanceof MongoError)) {
      // Node.js or some other error we have not special handling for
      return error as Error;
    }

    if (connectionIsStale(this.pool, connection)) {
      return error;
    }

    const session = options?.session;
    if (error instanceof MongoNetworkError) {
      if (session && !session.hasEnded && session.serverSession) {

View on GitHub (pinned to 3366c21a63)

Solutions

1. Update to the latest driver patch release; many such paths were hardened.
2. Audit any custom auth, monitoring, or stream code you inject for non-Error rejections and wrap them in Error instances.
3. Report the issue with the command and stack trace if it reproduces on the latest version.

Example fix

// before (custom transport)
socket.on('error', () => { throw 'broken pipe'; });
// after
socket.on('error', (e) => { throw new Error('broken pipe: ' + e?.message); });

function isErrorLike(e) {
  return typeof e === 'object' && e !== null && 'name' in e;
}

try {
  await coll.findOne(filter);
} catch (e) {
  if (!isErrorLike(e)) {
    // log and rethrow a normalized Error
    throw new Error('Non-Error thrown from driver: ' + String(e));
  }
  throw e;
}

When it happens

Trigger: A promise rejection deep in the connection or auth layer with a non-Error value (`throw 'timeout'`, `reject(42)`); a custom auth plugin or stream transform that rejects with a string; a null error propagated from a closed socket handler.

Common situations: Third-party auth/transport code throwing primitives; an older driver version with an unfixed bug; corrupted/incomplete error objects from native addons.

Related errors

• Unexpected HostAddress ${JSON.stringify(hostAddress)}
• ServerSessionPool requires a MongoClient
• Unrecognized options
• Unreachable. If you are seeing this error, please file a tic
• Attempted illegal state transition from [${this.state}] to [

AI-assisted analysis of mongodb/node-mongodb-native@3366c21a63 (2026-08-04). Data as JSON: /data/errors/f59540496a235a1d.json. Report an issue: GitHub.