Flutter Web: BigInt

Avoiding precision loss in the browser.

Flutter Web compiles to JavaScript, which means it shares the same 64-bit float limitations as any other JS application.

The Problem

If you parse a large Memo ID (near 18,446,744,073,709,551,615) as an int in Dart when running on Web, you will lose precision. Dart int compiles to a JS Number, which is only exact up to Number.MAX_SAFE_INTEGER (9,007,199,254,740,991). For example, int.parse('9007199254740993') silently becomes 9007199254740992 — one unit off, with no error.

The Solution

The Dart package uses BigInt internally and returns the routingId as a String.

Never convert the routingId to an int if your app targets Web. Always keep it as a String or a BigInt.

The Built-In Safety Net (v1.1.0+)

The package now ships a dedicated web-safe layer so you do not have to hand-roll these guards:

• isWebJsRuntime — a compile-time (conditional-import) probe that is true only when your app is compiled to JavaScript.
• SafeRoutingId — a BigInt-backed wrapper that parses, validates, compares, and serializes 64-bit routing IDs as exact decimal strings. It never routes the value through int/JS Number, and fromInt rejects values above Number.MAX_SAFE_INTEGER on web builds instead of propagating a truncated number.
• RoutingResult.idString / RoutingResult.safeId — web-safe accessors for the resolved routing ID.

final id = SafeRoutingId.parse('9007199254740993'); // 2^53 + 1
id.value;              // '9007199254740993' — exact in the browser
id.toJson();           // '9007199254740993' — safe to jsonEncode
id.exceedsJsSafeRange; // true

Browser-only test vectors in packages/core-dart/test/web_compat/routing_id_web_test.dart pin the boundary IDs (2^53 - 1, 2^53, 2^53 + 1, 2^63 - 1, 2^63, 2^64 - 1) through memo extraction, muxed decode, and JSON serialization. Run them with:

cd packages/core-dart
dart test test/web_compat --platform chrome