my colourful logger

log.js

import R from 'ramda';

const levels = {
  debug: 0,
  log: 1,
  info: 2,
  warn: 3,
  error: 4
};

const outputLevel = levels[process.env.LOG_LEVEL] || levels.debug;
const outputColor = (() => {
  const chromeRegexp = /Chrome\/(\d+)/;
  const matches = chromeRegexp.exec(navigator.userAgent);
  return matches && Number(matches[1]) >= 24;
})();

const levelNames = Object.keys(levels);

/* eslint-disable no-console */
const debugHandler = (...args) => console.debug(...args);
const logHandler = (...args) => console.log(...args);
const infoHandler = (...args) => console.info(...args);
const warnHandler = (...args) => console.warn(...args);
const errorHandler = (...args) => console.error(...args);
/* eslint-enable no-console */

const handlers = [
  debugHandler, // debug
  logHandler, // log,
  infoHandler, // info,
  warnHandler, // warn
  errorHandler // error
];

const styles = [
  'background: white; color: gray; padding: 0 0 0 1em;', // debug
  'background: lightgray; color: black; padding: 0 1em;', // log
  'background: blue; color: white; padding: 0 1em;', // info
  'background: white; color: red; padding: 0 0 0 1em;', // warn
  'background: red; color: black; padding: 0 1em;' // error
];

const log = R.curryN(3, function log(tag, level, message, data) {
  if (!console.log || (process.env.NODE_ENV === 'production' && !/debug/.test(window.location.href)) || level < outputLevel) {
    return;
  }

  const handler = handlers[level];
  let args;

  if (outputColor) {
    args = [
      `%c${tag}%c${levelNames[level]}%c${message}`,
      'background: black; color: white; padding: 0 1em;',
      styles[level],
      'background: white; color: green; padding-left: 1em;'
    ];
  } else {
    args = [
      `${tag}: ${levelNames[level]}: ${message}`
    ];
  }

  if (data) {
    args = args.concat([R.clone(data)]);
  }

  handler(...args);
});

export {
  levels,
  log
};

usage.js

import {log, levels as logLevels} from './log';

const logger = log('MyApplication');
const debugFn = logger(levels.debug);

debugFn("Description");
debugFn("Description", {some: 'metadata'});