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Version: Next

jslog vs Go slog

How jslog compares to Go's log/slog package.

Core Compatibility​

jslog implements the complete Go slog API:

FeatureGo slogjslogStatus
slog.Debug()YesYesImplemented
slog.Info()YesYesImplemented
slog.Warn()YesYesImplemented
slog.Error()YesYesImplemented
slog.New()YesYesImplemented
slog.Default()YesYesImplemented
slog.SetDefault()YesYesImplemented
slog.With()YesYesImplemented
slog.WithGroup()YesYesImplemented
slog.TextHandlerYesYesImplemented
slog.JSONHandlerYesYesImplemented
slog.LevelYesYesImplemented
slog.LevelVarYesYesImplemented
Handler interfaceYesYesImplemented
ReplaceAttrYesYesImplemented

Features jslog Has That Go slog Doesn't​

1. ColorHandler​

Beautiful ANSI color-coded console output:

const logger = New(new ColorHandler());
logger.error('Critical error detected');  // Red!

Go slog: Requires third-party packages.

2. FileHandler with Rotation​

Built-in file logging with automatic rotation:

const logger = New(new FileHandler({
  filepath: './logs/app.log',
  maxSize: 10 * 1024 * 1024,  // 10MB
  maxFiles: 5
}));

Go slog: Requires external libraries like lumberjack.

3. BufferedHandler​

Batch log writing for better performance:

const logger = New(new BufferedHandler({
  handler: new JSONHandler(),
  bufferSize: 100,
  flushInterval: 1000
}));

Go slog: Manual buffering implementation required.

4. SamplingHandler​

Probabilistic sampling for high-traffic apps:

const logger = New(new SamplingHandler({
  handler: new TextHandler(),
  rate: 0.1  // Log 10% of messages
}));

Go slog: Custom handler wrapper needed.

5. FilterHandler​

Advanced filtering beyond level-based filtering:

const logger = New(new FilterHandler({
  handler: new ColorHandler(),
  filter: (record) => record.level >= Level.ERROR || record.message.includes('critical')
}));

Go slog: Custom handler implementation required.

6. AsyncHandler​

Non-blocking log operations:

const logger = New(new AsyncHandler({
  handler: new FileHandler({ filepath: './logs/app.log' }),
  errorHandler: (err) => console.error('Log error:', err)
}));

Go slog: While Go has goroutines, explicit async patterns require manual setup.

7. Middleware Pattern​

Composable handler middleware:

const logger = New(new MiddlewareHandler({
  handler: new JSONHandler(),
  middleware: [
    hostnameMiddleware(),
    pidMiddleware(),
    dedupeMiddleware(1000),
    rateLimitMiddleware(100)
  ]
}));

Go slog: Handler wrapping pattern must be manually implemented.

8. Built-in Metrics​

Automatic logging statistics:

const metrics = new MetricsMiddleware();
const logger = New(new MiddlewareHandler({
  handler: new JSONHandler(),
  middleware: [metrics.middleware()]
}));

// Later...
console.log(metrics.getStats());

Go slog: No built-in metrics.

9. Deduplication​

Automatic spam prevention:

const logger = New(new MiddlewareHandler({
  handler: new ColorHandler(),
  middleware: [dedupeMiddleware(1000)]
}));

logger.info('Repeated message');  // Shows
logger.info('Repeated message');  // Deduplicated!

Go slog: Manual implementation needed.

10. Rate Limiting​

Automatic rate limiting:

const logger = New(new MiddlewareHandler({
  handler: new TextHandler(),
  middleware: [rateLimitMiddleware(100)]  // Max 100/second
}));

Go slog: Manual rate limiting required.

11. Fluent Attribute Builder​

Chain attributes easily:

const attrs = attrs()
  .str('user', 'alice')
  .num('age', 30)
  .bool('active', true)
  .if(condition, 'conditional', 'value')
  .build();

logger.info('User created', ...attrs);

Go slog: No fluent API.

12. Performance Timers​

Built-in timing utilities:

const timer = startTimer('operation');
// ... do work ...
logger.info('Operation complete', timer.elapsed());

Go slog: Manual timer implementation needed.

13. Correlation IDs​

Global request/trace tracking:

setCorrelationId('trace-123');

logger.info('Request 1', CorrelationId());  // Includes trace-123
logger.info('Request 2', CorrelationId());  // Includes trace-123

Go slog: Manual context management required.

14. HTTP Helpers​

Easy request/response logging:

logger.info('HTTP request', ...HttpReq({
  method: 'POST',
  url: '/api/users',
  ip: '192.168.1.1'
}));

logger.info('HTTP response', ...HttpRes({
  status: 201,
  duration: 45,
  size: 1024
}));

Go slog: Manual attribute construction.

15. System Info​

Environment and memory helpers:

logger.info('App started', ...EnvInfo());
logger.info('Memory status', ...MemoryUsage());

Go slog: Manual info gathering.

16. Data Masking​

Built-in PII redaction:

logger.info('User data',
  String('email', maskEmail('alice@example.com')),  // a***@example.com
  String('card', maskCreditCard('4532-1234-5678-9010'))  // ****-****-****-9010
);

Go slog: Manual masking functions needed.

17. Stack Traces​

Automatic stack trace capture:

logger.error('Error occurred', StackTrace());

Go slog: Manual stack trace capture.

18. Caller Info​

Automatic source location:

logger.info('Log with caller', Caller());
// Includes file and line number

Go slog: Has addSource but limited.

19. Error Boundaries​

Catch handler errors safely:

const logger = New(new MiddlewareHandler({
  handler: new JSONHandler(),
  middleware: [errorBoundaryMiddleware()]
}));

Go slog: Manual error handling needed.

20. Circular Reference Handling​

Safe JSON serialization:

const circular = { a: 1 };
circular.self = circular;

logger.info('Data', Any('obj', circular));  // Safely handled!

Go slog: Would panic on circular references.

Summary​

jslog gives you everything Go's slog has, plus 20+ additional features specifically designed for Node.js production environments!

When to Use jslog​

You should use jslog if:

  • You want Go's slog API in Node.js
  • You need production-ready logging features
  • You want file rotation, buffering, sampling
  • You need async handlers and middleware
  • You want built-in utilities and helpers

You came from Go and want familiar logging:

  • API-compatible with Go's slog
  • Same mental model and patterns
  • Easy transition for Go developers

Next Steps​