Node Winston

A set of winston formats, console transport and logger creation functions.

Simplifies using winston logging and provides coloured YAML log output for local development.

Creating a Logger

The createLogger function combines omitFormat, omitNilFormat and optionally prettyConsoleFormat together to configure the Console transport for the returned logger.

| Option | Description | | ---------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | | consoleFormat | Either pretty (useful for local development) or json (default) | | consoleOptions | The ConsoleTransportOptions passed into the Console transport, useful for setting silent, e.g. to switch off output during test runs, per-transport level etc. | | loggerOptions | The LoggerOptions passed into the Logger, useful for the level, defaultMeta and other customisations. | | loggerOptions | The LoggerOptions passed into the Logger, useful for the level, defaultMeta and other customisations. | | omitPaths | Paths of fields you wish to omit form logging. For example, during local development you may wish to hide values from defaultMeta, e.g. user context which would be omitted in every log entry and irrelevent for local dev. | | transports | Extra Transports you wish to add to the logger. |

At MakerX we generally use config files to control logging output across local development and deployed environments:

logger.ts

import { isLocalDev } from '@makerxstudio/node-common'
import { createLogger } from '@makerxstudio/node-winston'
import config from 'config'

const logger = createLogger({
  consoleFormat: isLocalDev ? 'pretty' : 'json',
  consoleOptions: config.get('logging.consoleOptions'),
  loggerOptions: config.get('logging.loggerOptions'),
  omitPaths: config.get('logging.omitPaths'),
})

export default logger

This would translate into different runtime configurations:

// local development logger would be created something like...
const logger = createLogger({
  consoleFormat: 'pretty',
  loggerOptions: {
    defaultMeta: {
      service: 'my-application-name',
    },
    level: 'verbose',
  },
  omitPaths: ['service'], // defaultMeta.service is set in the default (all environments) config, localdev config strips this from output
})

// deployed environment logger would be created something like...
const logger = createLogger({
  consoleFormat: 'json',
  loggerOptions: {
    defaultMeta: {
      service: 'my-application-name',
    },
    level: 'info',
  },
})

// integration tests could silence noisy console output by setting process.env.SILENT_CONSOLE to 'true'
const logger = createLogger({
  consoleOptions: {
    silent: true,
  },
})

Transports

The createLogger method creates (only) a Console transport.

If you wish to add other transports, pass them in via the transports option, e.g.

const logger = createLogger({
  transports: [
    new DailyRotateFile({
      level: 'info',
      filename: 'application-%DATE%.log',
      datePattern: 'YYYY-MM-DD-HH',
      zippedArchive: true,
      maxSize: '20m',
      maxFiles: '14d',
    }),
  ],
})

Formats

createLogger applies some default behaviour, chaining omitNilFormat and omitFormat in front of the final json or coloured YAML format.

• omitNilFormat removes null or undefined values from output
• omitFormat removes values by path using lodash omit (see docs for path specification)
• prettyConsoleFormat applies the colorize and timestamp formats before formatting logs as coloured YAML

If you wish to add additional formats, pass them in via the consoleFormats option.

Error serialization

The Error class's message and stack properties are not enumerable; the output of JSON.stringify(new Error('message')) is '{}'.

Winston has some special handling, so that when an error is the first or second argument, message and stack props are logged:

logger.log(new Error('cause')) // {message: 'cause', stack: ...}
logger.log('message', new Error('cause')) // {message: 'message cause', stack: ...}

However, when errors are nested in structured log data, message and stack props are lost:

catch (error) {
  logger.log('message', { info, error }) // {message: 'message', error: {}}
}

Winston logform uses safe-stable-stringify which supports a replacer, similar to JSON.stringify.

In createLogger we use serializableErrorReplacer via the JSON format options to ensure that the message and stack properties of errors are serialized to error logs:

format.json({ replacer: serializableErrorReplacer })