Zerg

Lightweight logging library for apps and libs

Futures

• Zero dependencies
• TypeScript support
• Easy to use
• Custom listeners/transports
• Support Node.js and Browsers

Getting started

Installation

npm i --save zerg

or

yarn add zerg

Usage

Make module logger.js:

import zerg from 'zerg';
import {
  consoleNodeColorful,
  consoleBrowserColorful,
} from 'zerg/dist/transports';
const logger = zerg.createLogger();
// Add console logger
const listener = zerg.createListener({
  handler: consoleBrowserColorful, // for browser
  // handler: consoleNodeColorful, // for node
});
logger.addListener(listener);
export default logger;

Make your module and import logger.js:

import logger from './logger';
const log = logger('moduleName');
log.verbose('verbose message');
log.debug('debug message');
log.info('info message');
log.warn('warn message');
log.error('error message', {foo: 'bar'});

Result:

API

Types

type TExtendedData = Record<string, any>;

type TLogMessage = {
  timestamp: number;
  loggerName: string;
  moduleName: string;
  level: TLogLevel;
  message: string;
  extendedData?: TExtendedData
};

type LogLevel = 'verbose' | 'debug' | 'info' | 'warn' | 'error';

type Listener = (log: TLogMessage) => void;

zerg.createLogger(): Logger - Create logger instance

zerg.createListener(params): LogListener - Create listener for logger

• params.handler: (logMessage: TLogMessage) => void;
• params.filter?: (logMessage: TLogMessage) => boolean; (optional)
• params.levels?: LogLevel; (optional)

logger.addListener(listener: LogListener)

import zerg from 'zerg';
const logger = zerg.createLogger();
const listener = zerg.createListener({
  handler: (logMessage) => console.log(logMessage),
  levels: ['info'], // listen only `info` level
});
logger.addListener(listener);
logger.module('myModule').info('Info message', {foo: 'bar'});
logger.module('myModule').warn('Warn message', {bar: 'baz'});
logger.module('myModule').error('Error message');
/* console
{
  timestamp: 1467967421933,
  level: 'info',
  moduleName: 'myModule',
  message: 'Info message',
  extendedData: {foo: 'bar'},
}
*/

Use filter - Listen messages only from “Sarah” module

import zerg from 'zerg';
const logger = zerg.createLogger();
const listener = zerg.createListener({
  handler: (logMessage) => console.log(logMessage),
  filter: (logMessage) => logMessage.moduleName === 'Sarah', // listen messages only from "Sarah" module
  // levels: [], // at this case levels are ignoring
});
logger.addListener(listener);
logger.module('Alice').info('Info message', {foo: 'bar'});
logger.module('Bob').warn('Warn message', {bar: 'baz'});
logger.module('Sarah').error('Error message');
/* console
{
  timestamp: 1467967421933,
  level: 'info',
  moduleName: 'myModule',
  message: 'Info message',
  extendedData: {foo: 'bar'},
}
*/

removeListener(LogListener): void;

removeAllListeners(): void;

module(moduleName: string): LoggerModule;

getModule(moduleName: string): LoggerModule | null;

getModules(): Record;

Other Examples

Sentry transport

import zerg from 'zerg';
const logger = zerg.createLogger();
const SENTRY_LEVEL_MAP = {
  info: 'info',
  warn: 'warning',
  error: 'error',
  fatal: 'error',
};
function sentryTransport(logMessage) {
  const level = SENTRY_LEVEL_MAP[logMessage.level];
  Sentry.withScope((scope) => {
    scope.setLevel(level);
    Object.keys(logMessage.extendedData).forEach((key) => {
      scope.setExtra(key, logMessage.extendedData[key]);
    });
    scope.setTag('module', logMessage.moduleName);
    Sentry.captureMessage(logMessage.message);
  });
}
const listener = zerg.createListener({handler: sentryTransport});
logger.addListener(listener);

Remote debug transport

It is be useful for debug when browser (or device) doesn’t provide tool: Android with default browser, WinPhone, SmartTV.

At browser:

import zerg from 'zerg';
const logger = zerg.createLogger();
function remoteTransport(logMessage) {
  const req = new XMLHttpRequest();
  req.open('POST', 'http://myhost.com:3000/log', false);
  req.setRequestHeader('Content-type', 'application/json');
  req.send(JSON.stringify(logMessage));
}
const listener = zerg.createListener({handler: remoteTransport});
logger.addListener(listener);

Don’t forget, host (http://myhost.com:3000/log) must be reachable from device.

At server you may use express:

const express = require('express');
const bodyParser = require('body-parser');
const app = express();
app.use(bodyParser.json()); // for parsing application/json
app.post('/log', (req, res) => {
  console.log(req.body);
});
app.listen(3000);