Logger

Log app activity using different transports.

Install

npm install @universal-packages/logger

Logger

A logger object job is to be an interface for what the user wants to log and pass that information through all configured transports. It will apply the following rules before passing the log entry to the transports.

It will apply the following rules before passing the log entry to the transports:

1. Checks if the logger is not silent if it is it will not do anything with the log entry
2. Check if the log entry is inside the configured log level threshold
3. To ensure every log is dispatched after the other we use a buffer dispatcher that awaits until the transport finishes processing the log entry and then continue with the next one.

By default a logger transports are a TerminalTransport and a LocalFileTransport.

import { Logger } from '@universal-packages/logger'

const logger = new Logger({ transports: ['terminal', 'local-file'] })

logger.log({ level: 'INFO', title: 'We are online' })

// > 001 INFO 7:43:05 PM
// > We are online

Options

• level LogLevel | LogLevel[] If you specify a level here the logger will only log entries with the same level of importance and below, or you can specify an array of levels, it will only log entries in those levels.

  The level of importance if the following, with 0 for the most important

  0. FATAL
  1. ERROR
  2. WARNING
  3. INFO
  4. QUERY
  5. DEBUG
  6. TRACE

  For example if you specify WARNING as level the logger will only log entries with level WARNING, ERROR and FATAL

  You can also specify an array of levels in case you want an arbitrary group of log entries to be logged, for example if you specify ['INFO', 'QUERY'], only those kind of log entries will be processed.

• silence boolean Set this as true if you want the logger to not process any log entries.

• transports (string | Object)[] List of transports to pass entries to, a selection of all available transports than can be loaded.

  import { LocalFileTransport, TerminalTransport } from '@universal-packages/logger'
  
  const logger = new Logger({ transports: [{ transport: 'terminal', transportOptions: { clear: true } }] })

• includeTransportAdapters object An object with the transport name as key and the adapter object class as value, this is useful to pass the adapter to the logger that can not be loaded with the adapter resolver subsystem.

  import { MyTransport } from './MyTransport'
  
  const logger = new Logger({
    transports: ['my-transport'],
    includeTransportAdapters: { 'my-transport': MyTransport }
  })

• filterMetadataKeys String[] default: ['secret', 'password', 'token'] Before passing metadata to transports it will filter the value of these keys in the metadata object to <filtered>

Instance methods

log(entry: Object, [configuration: Object])

Passes a log entry to the transports to be processed.

waitForLoggingActivity()

Returns a promise that resolves when all log entries have been processed by the transports.

entry

All the information and level that an event carries to be logged.

• level 'FATAL' | 'ERROR' | 'WARNING' | 'INFO' | 'QUERY' | 'DEBUG' | 'TRACE' Log level to which this log entry belongs.

• title string A quick and concise description of the event to be logged.

• message string Additional information about the event.

• error Error If this is an ERROR level log entry you can pass the error object here.

• category string Useful to categorize logs apart from others, will be passed to all log entries.

• measurement number | string | Measurement A number representing a measurement made for the event commonly in milliseconds,formatted string or a Measurement object.

• metadata {} Additional information related to the event, an object with related data.

• tags string[] Additional information related to the event, an array of tags to classify even further this event.

configuration

Any additional configuration to be passed to the transports about the log entry. For example to tell the Terminal transport to use a category color.

logger.log({ level: 'INFO', title: 'We are online', category: 'SOCKET' }, { categoryColor: 'GREEN' })

Getters

dispatcher

A reference to the internal buffer dispatcher that will process the log entries.

Transport

To create a transport that suits your requirements you just need to implement new classes and use them as the following:

import MyTransport from './MyTransport'

const logger = new Logger({ transports: [{ transport: new MyTransport() }] })

The log method of the transport will be called with TransportLogEntry object.

export default class MyTransport {
  constructor(options) {
    // Options passed through the adapters sub system
  }

  prepare() {
    // Initialize any connection using options
  }

  release() {
    // Release any resources or close any connection
  }

  log(entry, configuration) {
    // Process the log entry
  }
}

TransportLogEntry

An object containing all the log entry information to be transported to your fancy log system, extending from LogEntry

• environment Date Teh environment the app is running NODE_ENV

• timestamp Date A date representing the moment a log entry is logged.

• index number The number of log entries that have been logged since the logger started logging.

TransportInterface

If you are using TypeScript just implement the TransportInterface in your class to ensure the right implementation.

import { TransportInterface } from '@universal-packages/logger'

export default class MyEngine implements TransportInterface {}

TerminalTransport

This logger provided terminal printing transport.

import { Logger, TerminalTransport } from '@universal-packages/logger'

const transport = new TerminalTransport()
const logger = new Logger({ transports: { terminal: transport } })

logger.log({ level: 'INFO', title: 'We are online' })

// > 001 INFO 7:43:05 PM
// > We are online

Options

• clear boolean If true the terminal screen will be cleared before the first log entry is printed.

• categoryColor 'BLACK' | 'RED' | 'YELLOW' | 'PURPLE' | 'BLUE' | 'GRAY' | 'DARK' | 'GREEN' | 'AQUA' | 'KIWI' Color scheme to use when printing the logger category

LocalFileTransport

This logger provided file appending transport, the usual logs/environment.log with all logs in it, the environment file name selected from the TransportLogEntry.

import { LocalFileTransport, Logger } from '@universal-packages/logger'

const transport = new LocalFileTransport()
const logger = new Logger({ transport })

logger.log({ level: 'INFO', title: 'We are online' })

// *** In file logs/environment.log
// > 001 INFO 7:43:05 PM
// > We are online

Options

• asJson boolean If true lines in the file will only be the serialized TransportLogEntry.

• logsLocation string By default logs will be created in ./logs but this can be changed here.

Typescript

This library is developed in TypeScript and shipped fully typed.

Contributing

The development of this library happens in the open on GitHub, and we are grateful to the community for contributing bugfixes and improvements. Read below to learn how you can take part in improving this library.

• Code of Conduct
• Contributing Guide

License

MIT licensed.