LogLayer

Basic Logging ​

LogLayer provides a simple and consistent API for logging messages at different severity levels. This guide covers the basics of logging messages.

Log Levels ​

LogLayer supports six standard log levels, each with its own method:

  • info() - For general information messages
  • warn() - For warning messages
  • error() - For error messages
  • debug() - For debug information
  • trace() - For detailed debugging information
  • fatal() - For critical errors that require immediate attention

Unsupported Log Levels

Some logging libraries may not support all levels. In such cases:

  • trace is mapped to debug
  • fatal is mapped to error

Basic Message Logging ​

The simplest way to log a message is to use one of the log level methods:

typescript
// Basic info message
log.info('User logged in successfully')

// Warning message
log.warn('API rate limit approaching')

// Error message
log.error('Failed to connect to database')

// Debug message
log.debug('Processing request payload')

// Trace message (detailed debugging)
log.trace('Entering authentication function')

// Fatal message (critical errors)
log.fatal('System out of memory')

Message Parameters ​

All log methods accept multiple parameters, which can be strings, booleans, numbers, null, or undefined:

typescript
// Multiple parameters
log.info('User', 123, 'logged in')

// With string formatting
log.info('User %s logged in from %s', 'john', 'localhost')

sprintf-style formatting

The logging library you use may or may not support sprintf-style string formatting. If it does not, you can use the sprintf plugin to enable support.

Message Prefixing ​

You can add a prefix to all log messages either through configuration or using the withPrefix method:

typescript
// Via configuration
const log = new LogLayer({
  prefix: '[MyApp]',
  transport: new ConsoleTransport({
    logger: console
  })
})

// Via method
const prefixedLogger = log.withPrefix('[MyApp]')

// Output: "[MyApp] User logged in"
prefixedLogger.info('User logged in')

Enabling/Disabling Logging ​

You can control whether logs are output using these methods:

typescript
import type { LogLevel } from 'loglayer'

// Disable all logging
log.disableLogging()

// Enable logging again
log.enableLogging()

// Enable or disable specific log levels individually
log.enableIndividualLevel(LogLevel.debug)  // Enable only debug logs
log.disableIndividualLevel(LogLevel.debug) // Disable only debug logs

// Enable or disable log levels following the conventional log level hierarchy
log.setLevel(LogLevel.warn)  // Enable warn, error, and fatal (disable info, debug, trace)

Transport log levels

Be aware that transports may have their own log level settings. For example, if LogLayer is set to debug but the transport is set to error, the transport will only handle error and fatal messages.

Log Level Hierarchy ​

Log levels follow a hierarchy:

  • fatal (10) > error (20) > warn (30) > info (40) > debug (50) > trace (60)

When using setLevel(), all levels below it are also enabled.

For example, if you set the log level to warn:

  • warn, error, and fatal messages will be logged
  • info, debug, and trace messages will be ignored.

You can also ignore the hierarchy by using enableIndividualLevel() and disableIndividualLevel() methods to enable or disable specific log levels.

Checking if a Log Level is Enabled ​

You can check if a specific log level is enabled using the isLevelEnabled method:

typescript
if (log.isLevelEnabled(LogLevel.debug)) {
  log.debug('Debugging is enabled')
} else {
  log.info('Debugging is disabled')
}