Comparison with default object in optional parameter fails in JS release build

[rebaz94]

I encountered a strange issue where code that works fine in dev mode (and in native builds) fails in the JS release build.

The issue seems to happen when using a function that takes an optional parameter defaulting to an object (freezed), and comparing it like disabled == freezed.
In JS release mode, that comparison always fails, even when the value should match.

Example 1

This example uses a simple class without code generation — it works correctly in all modes.

const freezed = Object();

enum BlockTag { unset }

abstract class FnData1 {
  FnData1 withUpdateOf({
    BlockTag? blockTag = BlockTag.unset,
    String? description,
    Object? disabled,
    List<String>? content,
  });

  bool? get isDisabled;
}

class Example implements FnData1 {
  final int id;
  final bool? disabled;

  Example({required this.id, this.disabled});

  // Simulates what Freezed would generate
  Example copyWith({required int id, required bool? disabled}) {
    return Example(id: id, disabled: disabled);
  }

  @override
  FnData1 withUpdateOf({
    BlockTag? blockTag = BlockTag.unset,
    String? description,
    Object? disabled = freezed,
    List<String>? content,
  }) {
    return copyWith(
      id: id,
      disabled: disabled == freezed
          ? this.disabled
          : disabled == true
              ? true
              : null,
    );
  }

  @override
  bool? get isDisabled => disabled;

  @override
  String toString() => 'Example(id: $id, disabled: $disabled)';
}

void main() {
  final data = Example(id: 1, disabled: true);
  final updated1 = data.withUpdateOf();
  print('update1: disabled: ${updated1.isDisabled}, correct: ${updated1.isDisabled == true}'); // should be true

  final updated2 = data.withUpdateOf(disabled: false); // should set disabled = null
  print('update2: disabled: ${updated2.isDisabled}, correct: ${updated2.isDisabled == null}'); // should be null

  print('-------');

  final FnData1 data2 = Example(id: 1, disabled: true);
  final updated3 = data2.withUpdateOf();
  print('update3: disabled: ${updated3.isDisabled}, correct: ${updated3.isDisabled == true}'); // should be true

  final updated4 = data2.withUpdateOf(disabled: false); // should set disabled = null
  print('update4: disabled: ${updated4.isDisabled}, correct: ${updated4.isDisabled == null}'); // should be null
}

Example 2

This example uses a function generated by Freezed that implements FnData.
In this case, the comparison fails only in JS release mode.

part 'main.freezed.dart';

@freezed
class FnExample with _$FnExample implements FnData {
  FnExample._();

  factory FnExample({
    required String id,
    BlockTag? blockTag,
    String? description,
    bool? disabled,
  }) = _FnExample;

  factory FnExample.newInstance({required String id, bool? disabled}) {
    return FnExample(id: id, disabled: disabled);
  }

  @override
  FnData withUpdateOf({
    String? id,
    BlockTag? blockTag = BlockTag.unset,
    String? description,
    Object? disabled = freezed,
  }) {
    return copyWith(
      id: id ?? this.id,
      parentId: parentId ?? this.parentId,
      blockTag: blockTag != BlockTag.unset ? blockTag : this.blockTag,
      description: description != null ? (description.isEmpty ? null : description.trim()) : this.description,
      disabled: disabled == freezed
          ? this.disabled
          : disabled == true
          ? true
          : null,
    );
  }
}



void main() {
  final FnData data3 = FnExample.newInstance(id: '1', disabled: true);
  final updated5 = data3.withUpdateOf();
  print('update5: disabled: ${updated5.disabled}, correct: ${updated5.disabled == true}'); // should be true, but it's false in JS release

  final updated6 = data3.withUpdateOf(disabled: false); // should set disabled = null
  print('update6: disabled: ${updated6.disabled}, correct: ${updated6.disabled == null}'); // should be null (works correctly)
}

Expected behavior

• disabled == freezed should evaluate consistently across all build modes.
• The first call (withUpdateOf()) should preserve the same disabled state as before.

[rebaz94]

Here the full example with freezed

main.dart:

import 'main.freezed.dart';

abstract class FnData {
  String get id;

  BlockTag? get blockTag;

  String? get description;

  /// Default is null or false
  bool? get disabled;

  /// update common property of the function
  FnData withUpdateOf({
    String? id,
    BlockTag? blockTag = BlockTag.unset, //
    String? description,
    Object? disabled,
  });
}

extension type const BlockTag._(int value) {
  static const unset = BlockTag._(0);
}

@freezed
class FnExample with _$FnExample implements FnData {
  FnExample._();

  factory FnExample({
    required String id,
    BlockTag? blockTag, //
    String? description,
    bool? disabled,
  }) = _FnExample;

  factory FnExample.newInstance({required String id, bool? disabled}) {
    return FnExample(id: id, disabled: disabled);
  }

  @override
  FnData withUpdateOf({
    String? id,
    BlockTag? blockTag = BlockTag.unset,
    String? description,
    Object? disabled = freezed,
  }) {
    return copyWith(
      id: id ?? this.id,
      blockTag: blockTag != BlockTag.unset ? blockTag : this.blockTag,
      description: description != null ? (description.isEmpty ? null : description.trim()) : this.description,
      disabled: disabled == freezed
          ? this.disabled
          : disabled == true
          ? true
          : null,
    );
  }
}

void main() {
  final FnData data3 = FnExample.newInstance(id: '1', disabled: true);
  final updated5 = data3.withUpdateOf();
  print('update5: disabled: ${updated5.disabled}, correct: ${updated5.disabled == true}'); // should be true

  final updated6 = data3.withUpdateOf(disabled: false); // should set disabled = null
  print('update6: disabled: ${updated6.disabled}, correct: ${updated6.disabled == null}'); // should be null
}

freezed file:

// coverage:ignore-file
// GENERATED CODE - DO NOT MODIFY BY HAND
// ignore_for_file: type=lint
// ignore_for_file: unused_element, deprecated_member_use, deprecated_member_use_from_same_package, use_function_type_syntax_for_parameters, unnecessary_const, avoid_init_to_null, invalid_override_different_default_values_named, prefer_expression_function_bodies, annotate_overrides, invalid_annotation_target, unnecessary_question_mark

part of 'main.dart';

// **************************************************************************
// FreezedGenerator
// **************************************************************************

T _$identity<T>(T value) => value;

final _privateConstructorUsedError = UnsupportedError(
  'It seems like you constructed your class using `MyClass._()`. This constructor is only meant to be used by freezed and you are not supposed to need it nor use it.\nPlease check the documentation here for more information: https://github.com/rrousselGit/freezed#adding-getters-and-methods-to-our-models',
);

/// @nodoc
mixin _$FnExample {
  String get id => throw _privateConstructorUsedError;
  BlockTag? get blockTag => throw _privateConstructorUsedError; //
  String? get description => throw _privateConstructorUsedError;
  bool? get disabled => throw _privateConstructorUsedError;

  /// Create a copy of FnExample
  /// with the given fields replaced by the non-null parameter values.
  @JsonKey(includeFromJson: false, includeToJson: false)
  $FnExampleCopyWith<FnExample> get copyWith =>
      throw _privateConstructorUsedError;
}

/// @nodoc
abstract class $FnExampleCopyWith<$Res> {
  factory $FnExampleCopyWith(FnExample value, $Res Function(FnExample) then) =
      _$FnExampleCopyWithImpl<$Res, FnExample>;
  @useResult
  $Res call({
    String id,
    BlockTag? blockTag,
    String? description,
    bool? disabled,
  });
}

/// @nodoc
class _$FnExampleCopyWithImpl<$Res, $Val extends FnExample>
    implements $FnExampleCopyWith<$Res> {
  _$FnExampleCopyWithImpl(this._value, this._then);

  // ignore: unused_field
  final $Val _value;
  // ignore: unused_field
  final $Res Function($Val) _then;

  /// Create a copy of FnExample
  /// with the given fields replaced by the non-null parameter values.
  @pragma('vm:prefer-inline')
  @override
  $Res call({
    Object? id = null,
    Object? blockTag = freezed,
    Object? description = freezed,
    Object? disabled = freezed,
  }) {
    return _then(
      _value.copyWith(
            id: null == id
                ? _value.id
                : id // ignore: cast_nullable_to_non_nullable
                      as String,
            blockTag: freezed == blockTag
                ? _value.blockTag
                : blockTag // ignore: cast_nullable_to_non_nullable
                      as BlockTag?,
            description: freezed == description
                ? _value.description
                : description // ignore: cast_nullable_to_non_nullable
                      as String?,
            disabled: freezed == disabled
                ? _value.disabled
                : disabled // ignore: cast_nullable_to_non_nullable
                      as bool?,
          )
          as $Val,
    );
  }
}

/// @nodoc
abstract class _$$FnExampleImplCopyWith<$Res>
    implements $FnExampleCopyWith<$Res> {
  factory _$$FnExampleImplCopyWith(
    _$FnExampleImpl value,
    $Res Function(_$FnExampleImpl) then,
  ) = __$$FnExampleImplCopyWithImpl<$Res>;
  @override
  @useResult
  $Res call({
    String id,
    BlockTag? blockTag,
    String? description,
    bool? disabled,
  });
}

/// @nodoc
class __$$FnExampleImplCopyWithImpl<$Res>
    extends _$FnExampleCopyWithImpl<$Res, _$FnExampleImpl>
    implements _$$FnExampleImplCopyWith<$Res> {
  __$$FnExampleImplCopyWithImpl(
    _$FnExampleImpl _value,
    $Res Function(_$FnExampleImpl) _then,
  ) : super(_value, _then);

  /// Create a copy of FnExample
  /// with the given fields replaced by the non-null parameter values.
  @pragma('vm:prefer-inline')
  @override
  $Res call({
    Object? id = null,
    Object? blockTag = freezed,
    Object? description = freezed,
    Object? disabled = freezed,
  }) {
    return _then(
      _$FnExampleImpl(
        id: null == id
            ? _value.id
            : id // ignore: cast_nullable_to_non_nullable
                  as String,
        blockTag: freezed == blockTag
            ? _value.blockTag
            : blockTag // ignore: cast_nullable_to_non_nullable
                  as BlockTag?,
        description: freezed == description
            ? _value.description
            : description // ignore: cast_nullable_to_non_nullable
                  as String?,
        disabled: freezed == disabled
            ? _value.disabled
            : disabled // ignore: cast_nullable_to_non_nullable
                  as bool?,
      ),
    );
  }
}

/// @nodoc

class _$FnExampleImpl extends _FnExample {
  _$FnExampleImpl({
    required this.id,
    this.blockTag,
    this.description,
    this.disabled,
  }) : super._();

  @override
  final String id;
  @override
  final BlockTag? blockTag;
  //
  @override
  final String? description;
  @override
  final bool? disabled;

  @override
  String toString() {
    return 'FnExample(id: $id, blockTag: $blockTag, description: $description, disabled: $disabled)';
  }

  @override
  bool operator ==(Object other) {
    return identical(this, other) ||
        (other.runtimeType == runtimeType &&
            other is _$FnExampleImpl &&
            (identical(other.id, id) || other.id == id) &&
            (identical(other.blockTag, blockTag) ||
                other.blockTag == blockTag) &&
            (identical(other.description, description) ||
                other.description == description) &&
            (identical(other.disabled, disabled) ||
                other.disabled == disabled));
  }

  @override
  int get hashCode =>
      Object.hash(runtimeType, id, blockTag, description, disabled);

  /// Create a copy of FnExample
  /// with the given fields replaced by the non-null parameter values.
  @JsonKey(includeFromJson: false, includeToJson: false)
  @override
  @pragma('vm:prefer-inline')
  _$$FnExampleImplCopyWith<_$FnExampleImpl> get copyWith =>
      __$$FnExampleImplCopyWithImpl<_$FnExampleImpl>(this, _$identity);
}

abstract class _FnExample extends FnExample {
  factory _FnExample({
    required final String id,
    final BlockTag? blockTag,
    final String? description,
    final bool? disabled,
  }) = _$FnExampleImpl;
  _FnExample._() : super._();

  @override
  String get id;
  @override
  BlockTag? get blockTag; //
  @override
  String? get description;
  @override
  bool? get disabled;

  /// Create a copy of FnExample
  /// with the given fields replaced by the non-null parameter values.
  @override
  @JsonKey(includeFromJson: false, includeToJson: false)
  _$$FnExampleImplCopyWith<_$FnExampleImpl> get copyWith =>
      throw _privateConstructorUsedError;
}

Environemnt:

Flutter 3.35.1 • channel stable • ssh://git@github.com/flutter/flutter.git
Framework • revision 20f8274939 (10 weeks ago) • 2025-08-14 10:53:09 -0700
Engine • hash 6cd51c08a88e7bbe848a762c20ad3ecb8b063c0e (revision 1e9a811bf8) (2 months ago) •
2025-08-13 23:35:25.000Z
Tools • Dart 3.9.0 • DevTools 2.48.0

[rebaz94]

@mraleph What really confuses me is that the code I shared works fine, but my real project (with the same definition) doesn’t.
Also found that in the interface definition, disabled had no default value. Adding a default fixes it in the JS release build, though it worked normally in dev and release for both JS and native.

[osa1]

@rebaz94 do you have a standalone repro? The repro seems to be missing a bunch of dependencies (BlockTag, freezed etc.).

[rebaz94]

@osa1 here's a complete example below. The BlockTag and other properties are just included to clarify that the function accepts multiple parameters.

The issue is that I can’t reproduce it separately outside the project. The only difference I’ve found is that if I remove the default value for a parameter in the interface class, any call to withUpdateOf fails and no longer matches the freezed object.

Let me know if there’s any additional information I can provide or another way to extract what you need.

import 'main.freezed.dart';

abstract class FnData {
  String get id;

  BlockTag? get blockTag;

  String? get description;

  /// Default is null or false
  bool? get disabled;

  /// update common property of the function
  FnData withUpdateOf({
    String? id,
    BlockTag? blockTag = BlockTag.unset, //
    String? description,
    Object? disabled,
  });
}

extension type const BlockTag._(int value) {
  static const unset = BlockTag._(0);
}

@freezed
class FnExample with _$FnExample implements FnData {
  FnExample._();

  factory FnExample({
    required String id,
    BlockTag? blockTag, //
    String? description,
    bool? disabled,
  }) = _FnExample;

  factory FnExample.newInstance({required String id, bool? disabled}) {
    return FnExample(id: id, disabled: disabled);
  }

  @override
  FnData withUpdateOf({
    String? id,
    BlockTag? blockTag = BlockTag.unset,
    String? description,
    Object? disabled = freezed,
  }) {
    return copyWith(
      id: id ?? this.id,
      blockTag: blockTag != BlockTag.unset ? blockTag : this.blockTag,
      description: description != null ? (description.isEmpty ? null : description.trim()) : this.description,
      disabled: disabled == freezed
          ? this.disabled
          : disabled == true
          ? true
          : null,
    );
  }
}

void main() {
  final FnData data3 = FnExample.newInstance(id: '1', disabled: true);
  final updated5 = data3.withUpdateOf();
  print('update5: disabled: ${updated5.disabled}, correct: ${updated5.disabled == true}'); // should be true

  final updated6 = data3.withUpdateOf(disabled: false); // should set disabled = null
  print('update6: disabled: ${updated6.disabled}, correct: ${updated6.disabled == null}'); // should be null
}

[mraleph]

@rebaz94 are you still facing this miscompilation?

@natebiggs is there something we can do to narrow it down?

[rebaz94]

@rebaz94 are you still facing this miscompilation?

Yes, it still happens when I remove the default value from the interface.

[rebaz94]

@mraleph here’s some info from the real project I tested.
If the interface doesn’t provide a default value and you call withUpdateOf from anywhere without passing disabled, it falls back to an object that isn’t equal to the constant Freezed object.

Profile and release builds both show the same result.
If you compile with -O0, everything works correctly even without a default value in the interface.

So it looks like an optimization issue causing the incorrect behavior.

[biggs0125]

This seems like a bug in either dart2js's type inference or SSA.

Can you verify which version of the Dart SDK you're using?

I'm curious what happens if within your file you define your own Freezed const and use that as the default value. Something like:

static const _myFreezed = Freezed();

@override
  FnData withUpdateOf({
    String? id,
    BlockTag? blockTag = BlockTag.unset,
    String? description,
    Object? disabled = _myFreezed,
  }) {
    return copyWith(
      id: id ?? this.id,
      blockTag: blockTag != BlockTag.unset ? blockTag : this.blockTag,
      description: description != null ? (description.isEmpty ? null : description.trim()) : this.description,
      disabled: disabled == _myFreezed
          ? this.disabled
          : disabled == true
          ? true
          : null,
    );
  }

Also curious what happens if you use identical instead of ==:

@override
  FnData withUpdateOf({
    String? id,
    BlockTag? blockTag = BlockTag.unset,
    String? description,
    Object? disabled = freezed,
  }) {
    return copyWith(
      id: id ?? this.id,
      blockTag: blockTag != BlockTag.unset ? blockTag : this.blockTag,
      description: description != null ? (description.isEmpty ? null : description.trim()) : this.description,
      disabled: identical(disabled, freezed)
          ? this.disabled
          : disabled == true
          ? true
          : null,
    );
  }

I'm wondering if the issue is with us not sharing the const object properly or if there's something about the Freezed class that makes it behave this way.

[rebaz94]

@biggs0125 Sorry, I missed your reply earlier. I'm still experiencing the same issue.

I created freezed1 and compared it to the original freezed using ==, which returns true.
However, when I compare disabled == with freezed1, the comparison still returns false.
Using identical() produces the same result.

Dart SDK: 3.9.0