Loggerr

A very simple logger.

Features:

• Synchronous output (great for cli's, browser and tools)
• Levels (built-in and customizable)
• Formatting (built-in and customizable)
• Loggerr is dependency free (formatters are not)
• Always captures stack trace on error logs
• Tiny filesize
• The cli formatter 🚀

Install

$ npm install --save loggerr

Usage

const log = require('loggerr')
log.error(new Error('My error message'))
// Thu Apr 16 2015 22:05:27 GMT-0500 (CDT) [error] - {"msg":"Error: My error message\n<STACK TRACE>"}

log.info('Something happened', {
  foo: 'info about what happened'
})
// Thu Apr 16 2015 22:05:27 GMT-0500 (CDT) [info] - {"msg":"Something happened","foo":"info about what happened"}

Log Levels

Each log level can be directed to a different output stream or disabled entirely. The default levels are as follows:

• emergency
• alert
• critical
• error
• warning (default)
• notice
• info
• debug

Constants are available for setting and referencing the levels and their streams. These constants are the all uppercase version of the level. Here is an example of setting the log level:

const logger = new Loggerr({
  level: Loggerr.DEBUG
})

logger.debug('Foo')
// Thu Apr 16 2015 22:05:27 GMT-0500 (CDT) [debug] - {"msg":"Foo"}

Customize Levels

You can fully customize the levels for your purposes. For example, here we implement pino compatible levels:

const log = new Loggerr({
  level: [ 'trace', 'debug', 'info', 'warn', 'error', 'fatal' ]
})

log.trace('Example trace log')

See the example of custom levels for cli output.

Log Formatting

Loggerr supports formatting via formatter functions. The default formatter outputs a timestamp, the log level and the messages formatted as json. But you can provide a custom formatter function with the formatter options. Formatter functions take three parameters: date, level, data. Say we want to output the log message with a color based on the level:

const Loggerr = require('loggerr')
const chalk = require('chalk')

const logger = new Loggerr({
  formatter: (date, level, data) => {
    var color
    switch (Loggerr.levels.indexOf(level)) {
      case Loggerr.EMERGENCY:
      case Loggerr.ALERT:
      case Loggerr.CRITICAL:
      case Loggerr.ERROR:
        color = chalk.red
        break
      case Loggerr.WARNING:
      case Loggerr.NOTICE:
        color = chalk.yellow
        break
      case Loggerr.INFO:
      case Loggerr.DEBUG:
        color = chalk.white
        break
    }
    return color(data.msg)
  }
})

There are a few built-in in formatters:

• default: Outputs date, level and json
• cli: Outputs the message and json data, colorized and formatted
• bunyan: Compatible format to bunyan
• browser: Relies on console.log, so just returns the data

For these built-in formatters can specify the string name of the formatter for built-in formatters:

const log = new Loggerr({
  formatter: 'cli'
})

To use the cli formatter you can require it and pass the formatter options:

const log = new Loggerr({
  formatter: require('loggerr/formatters/cli')
})

Unformatted/Pre-formatted logging

If you need to write raw logs without formatting there are two options:

1. writeLevel(level, msg, done): Will respect logging level but skip all formatting
2. write(level, msg, done): Will write logs regardless of level and skip all formatting

Output Streams

You can output each level to it's own stream. The method is simple, just pass an array of streams corresponding to each level as the streams option. The simplest way is to just map over Loggerr.levels, this is how we set the defaults:

new Loggerr({
  streams: Loggerr.levels.map(function (level, i) {
    return i > Loggerr.WARNING ? process.stdout : process.stderr
  })
})

The most useful reason to specify an output stream to to redirect logs to files. Here is an example of how to do that:

const logfile = fs.createWriteStream('./logs/stdout.log', {
  flags: 'a',
  encoding: 'utf8'
})

new Loggerr({
  streams: Loggerr.levels.map(() => logfile)
})

Debug Stream

You can also pass a debugStream which will receive all logs regardless of level. This is helpful when you want to send logs to a file which you can use in error reporting or debugging failures.

new Loggerr({
  debugStream: fs.createWriteStream('./logs/debug.log', {
    flags: 'a',
    encoding: 'utf8'
  })
})

Bundling with Rollup

There is a dynamic require in this library. If you intend to use this with a bundler (ex Rollup) you may need to configure it to include the correct formatter if you pass that option as a string (ex formatter: 'cli').

Example:

// rollup.config.js
const { nodeResolve } = require('@rollup/plugin-node-resolve');
const commonjs = require('@rollup/plugin-commonjs');

module.exports = {
  input: 'index.js',
  output: {
    file: 'bundle.js',
    format: 'commonjs'
  },
  plugins: [
    nodeResolve(),
    commonjs({
      dynamicRequireTargets: [
        './node_modules/loggerr/formatters/cli.js',
      ]
    })
  ]
};

The values above will change based on your application, but the main important thing is the dynamicRequireTargets configuration.

Contributing

Contributions are welcome! To get started contributing, ensure you have a modern Node.js version and run node --run setup. To run the tests run npm t, and to run the lint npm run lint [-- --fix]. When pushing commits, kindly use Conventional Commits but I will be sure to clean things up before we merge.