upd

example/lib/main.dart

@@ -34,12 +34,15 @@ ${result.rowDescription?.columns.map((e) => '    name = ${e.name}').join('\n')}
         ...result.rows.map(rowToPrettyString),
       ].join('\n\n'),
     );
-  } on JSError catch (e) {
+  } on TransactionError catch (e) {
     await client.end();
 
     return Response('''
 ${e.name}
 ${e.cause}
+  ${e.cause.name}
+  ${e.cause.cause}
+  ${e.cause.message}
 ${e.message}
 $e
 ''');

lib/deno_postgres_interop.dart

@@ -9,6 +9,7 @@ export 'src/command_type.dart';
 export 'src/connection.dart';
 export 'src/connection_options.dart';
 export 'src/encoded_arg.dart';
+export 'src/errors/transaction_error.dart';
 export 'src/isolation_level.dart';
 export 'src/notice.dart';
 export 'src/partial/partial_connection_options.dart';

lib/src/errors/postgres_error.dart

@@ -0,0 +1,6 @@
+import 'dart:js_interop';
+
+import 'package:deno_postgres_interop/src/errors/js_error.dart';
+
+@JS()
+class PostgresError extends JSError {}

lib/src/errors/transaction_error.dart

@@ -0,0 +1,17 @@
+import 'dart:js_interop';
+
+import 'package:deno_postgres_interop/src/errors/js_error.dart';
+import 'package:deno_postgres_interop/src/errors/postgres_error.dart';
+
+/// [deno-postgres@v0.17.0/TransactionError](https://deno.land/x/postgres@v0.17.0/client/error.ts?s=TransactionError).
+@JS()
+class TransactionError {
+  /// [js/Error/cause](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error/cause).
+  external PostgresError get cause;
+
+  /// [js/Error/message](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error/message).
+  external String get message;
+
+  /// [js/Error/name](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error/name).
+  external String get name;
+}