The best Javascript library for structured logging

Modern JavaScript applications demand structured logging. As application complexity increases, efficient log searching, analysis, and monitoring become paramount. However, many logging solutions surprisingly complicate this process.

Traditional JavaScript logging libraries suffer from a fundamental flaw: they prioritize string-based logging, treating structured data as an afterthought. This leads to significant problems in modern applications:

1. Inconsistent Data Structures: Log entries exhibit varying data formats, hindering large-scale log querying and analysis.
2. Weak Type Safety: Most loggers accept arbitrary objects as metadata, resulting in runtime errors and inconsistent data types.
3. Conflicting Concerns: Messages, data, and errors are often intermingled, complicating programmatic log parsing and processing.
4. Limited Contextual Support: Implementing application-wide context frequently requires manual string concatenation or complex object merging.
5. Rigid APIs: Simple tasks, such as including both error and metadata in a log entry, necessitate cumbersome workarounds.

Let's examine how popular logging libraries address these challenges:

Winston

// Mixing message and data without a clear structure
winston.info("Processing order", { orderId, userId, amount });

Bunyan

// Requires creating child loggers solely to add context
const orderLogger = logger.child({ orderId, userId });
orderLogger.info({ amount }, "Processing order");

Pino

// Similar issues – metadata and message are intermixed
logger.info({ orderId, userId, amount }, "Processing order");

While these libraries offer structured logging features, their string-first design proves cumbersome for modern, data-driven logging requirements. Each handles structured data differently, yet none provide a truly satisfactory solution.

A Superior Approach to Structured Logging

Imagine a logging library built from the outset for structured logging. One that enforces consistent log structures, ensures type safety, and cleanly separates various data types.

This is where LogLayer (MIT Licensed) excels. Here's how it manages the same logging task:

// Clean separation of concerns using a type-safe builder pattern
logger
  .withContext({ userId })  // application-wide context
  .withMetadata({          // request-specific data
    orderId,
    amount
  })
  .info("Processing order");

LogLayer's core focus is structured logging. It offers:

• A type-safe builder pattern API
• Clear separation of context, metadata, and messages
• Consistent structure across the entire application
• A robust plugin system for data transformation
• Support for multiple transports without altering log structure
• First-rate error handling and serialization

Let's explore how LogLayer resolves common logging problems:

Comprehensive Structured Data Support

LogLayer simplifies the inclusion of structured data in logs:

// Add context included in all logs
logger.withContext({
  service: "payment-api",
  version: "1.2.0"
});

// Add metadata for specific log entries
logger.withMetadata({
  orderId: "12345",
  amount: 99.99
}).info("Payment processed successfully");

First-Rate Error Handling

Error logging is a central feature with dedicated support:

try {
  // ... code that might throw an error
} catch (error) {
  logger.withError(error)
        .withMetadata({ userId: "123" })
        .error("Failed to process payment");
}

// Or log only the error
logger.errorOnly(error);

Flexible Configuration

LogLayer provides extensive configuration options:

• Custom error serialization
• Configurable field names for errors, context, and metadata
• Runtime logging enable/disable
• Multiple transport support
• A plugin system for extending functionality

Clean Builder Pattern API

The builder pattern results in an intuitive and chainable API:

// Mixing message and data without a clear structure
winston.info("Processing order", { orderId, userId, amount });

Conclusion

LogLayer introduces structure and consistency to application logging while maintaining flexibility and extensibility. Its comprehensive feature set and clean API make it ideal for applications requiring robust, structured logging capabilities.

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