Javascript SDK Logging

Provides a centralized LogManager and errorHandler for Javascript SDK packages.

Installation

``sh
npm install @optimizely/js-sdk-logging
`

Architecture

!Logging Architecture


- LogHandler - the component that determines where to write logs. Common log handlers
are ConsoleLogHandler or NoopLogHandler
- LogManager - returns Logger facade instances via LogManager.getLogger(name)
- LoggerFacade the internal logging interface available to other packages via LogManager.getLogger(name)

Usage


#### Using the logger

`typescript
import { getLogger } from '@optimizely/js-sdk-logging'

const logger = getLogger('myModule')
logger.log('warn', 'this is a warning')

logger.debug('string interpolation is easy and %s', 'lazily evaluated')

logger.info('info logging')
logger.warn('this is a warning')
logger.error('this is an error')

// info warn debug and error all support passing an Error as the last argument
// this will call the registered errorHandler
logger.error('an error occurred: %s', ex.message)

// also Error passes to errorHandler.handleError(ex)
logger.error('an error occurred: %s', ex.message, ex)

// if no message is passed will log ex.message
logger.error(ex)
`

#### Setting the log level

`typescript
import { LogLevel, setLogLevel } from '@optimizely/js-sdk-logging'

// can use enum
setLogLevel(LogLevel.ERROR)

// can also use a string (lowercase or uppercase)
setLogLevel('debug')
setLogLevel('info')
setLogLevel('warn')
setLogLevel('error')
`


#### Setting a LogHandler

`typescript
import { setLogHandler, ConsoleLogHandler } from '@optimizely/js-sdk-logging'

const handler = new ConsoleLogHandler({
logLevel: 'error',
prefix: '[My custom prefix]', // defaults to "[OPTIMIZELY]"
})

setLogHandler(handler)
`

#### Implementing a custom LogHandler

Perhaps you want to integrate Optimizely with your own logging system or use an existing library.

A valid LogHandler is anything that implements this interface

`typescript
interface LogHandler {
log(level: LogLevel, message: string): void
}
`

Example: integrating with Winston

`js
import winston from 'winston'
import { setLogHandler, LogLevel } from '@optimizely/js-sdk-logging'

const winstonLogger = winston.createLogger({
level: 'info',
format: winston.format.json(),
defaultMeta: { service: 'optimizely' },
transports: [
new winston.transports.File({ filename: 'combined.log' }),
],
})

/**
* Convert from optimizely log levels to winston
*/
function convertLogLevels(level) {
switch(level) {
case LogLevel.DEBUG:
return 'debug'
case LogLevel.INFO:
return 'info'
case LogLevel.WARNING:
return 'warning'
case LogLevel.ERROR:
return 'error'
default:
return 'silly'
}
}

setLogHandler({
log(level, message) {
winstoLogger.log({
level: convertLogLevels(level),
message,
})
}
})
`

$3

`typescript
interface LoggerFacade {
log(level: LogLevel | string, message: string): void

info(message: string | Error, ...splat: any[]): void

debug(message: string | Error, ...splat: any[]): void

warn(message: string | Error, ...splat: any[]): void

error(message: string | Error, ...splat: any[]): void
}

interface LogManager {
getLogger(name?: string): LoggerFacade
}

interface LogHandler {
log(level: LogLevel, message: string): void
}
``