Churchill logger core functionality

Usage no npm install needed!

<script type="module">
  import churchillCore from 'https://cdn.skypack.dev/@churchill/core';


Churchill Core

Churchill core is the actuall logger. By default we include @churchill/console as the default transport, but you might want to install additional transports like file, elastic, http or socket.


npm install @churchill/core
# or if you want to log to different transport then the default
npm install @churchill/core @churchill/console
npm install @churchill/core @churchill/file
npm install @churchill/core @churchill/elastic @elastic/elasticsearch
# ...


Setting up Churchill is easy. Simply call churchill with a list of transports and if you are happy with the default formatting, you can use the logger in your services.

// logger.js
const churchill = require("@churchill/core");
const Console = require("@churchill/console");
const File = require("@churchill/file");

const createNamespace = churchill({
  transports: [
    File.create({ filename: "error.log", maxLevel: "error" }),
    File.create({ filename: "combined.log" })

Here is an example service:

// worker-a.js
const logger = require('./logger')('worker:a')
logger.error('Got an error!', new Error('Err!'))
logger.info('Log me with some data!', { here: { are: 'some metadata' }})
// the default max log level is info (anything below will not be logged by default)
logger.debug( ... )
logger.silly( ... )

The default log levels contains 6 levels, that are ascending numerical values, where the lower the number the more important the log message is.

const LEVELS = {
  error: 0,
  warn: 1,
  info: 2, // Default maximum log level
  verbose: 3,
  debug: 4,
  silly: 5


This is the list of currently supported transports. Check the examples folder to see their usage. (Note that all transports are exported under churchill.trasports.<Transport>)

Name Description Example
Console Log to console Console.create({ errorLevel: "error", ... })
File Log to a file File.create({ filename: "error.log", level: "error", ... })
Stream Log to any arbitrary stream. Stream.create({ stream: <Stream>, ... })
HTTP Log to a HTTP stream. HTTP.create({ path: "https://domain.com/path", ... })
Elastic Log to an elasticsearch index. Elastic.create({ node: "http://localhost:9200", index: "logs", ... })
Socket* (*Not Implemented Yet) Log to a socket Socket.create({ host: "", port: 1337, ... })


Custom Log Levels

You can also specify custom levels.

const customLevels = {
  critical: 0,
  warning: 1,
  log: 2,
  debug: 3

const customColors = {
  critical: "red",
  warning: "orange",
  log: "blue",
  debug: "gray"

churchill({ levels: customLevels, colors: customColors });

Available colors are black, red, green, yellow, blue, magenta, cyan, white, gray, redBright, greenBright, yellowBright, blueBright, magentaBright, cyanBright, whiteBright. For more information check the chalk package.

Custom Formats

Churchill supports custom formatting functions. A formatting function accepts info (global format) or info, output, logger (transport format) objects which is the logged message, globally formatted message and the logger instance. The return value is what will be sent to transport streams.

const util = require("util");

const customGlobalFormat = info => {
  return { ...info, logger: "churchill:" };

const customFormat = info => {
  const { logger, namespace, timestamp, level, ms, args } = info;

  return `${logger}${namespace} ${level} ${args.map(arg => util.format(arg)).join(" ")} +${ms}ms`;

const createLogger = churchill({
  format: customGlobalFormat,
  transports: [Console.create({ format: customFormat })]

const loggerA = createLogger("worker:a");
const loggerB = createLogger("worker:b");
const loggerC = createLogger("worker:c");

loggerA.info("test", { metadata: "some info" });
// churchill:worker:a info test { metadata: 'some info' } +1ms
loggerB.info("test", { metadata: "some info" });
// churchill:worker:b info test { metadata: 'some info' } +0ms
loggerC.error("test", { metadata: "some info" });
// churchill:worker:c error test { metadata: 'some info' } +0ms

Custom transport

For implementing custom transport please see transport package.

Environmental Variables

You can change the funcionality of the logger by setting enviromental variables.

Variable Description
CHURCHILL_DEBUG List of enabled namespaces separated by a comma, can be also used with wildcard (i.e. worker:a*)
CHURCHILL_DEBUG_LEVEL Max. level to log (i.e. debug)

Logging Uncaught Exceptions

Simply add listener for the uncaughtException and log whatever you need.

process.on("uncaughtException", err => {
  // Note: if you use any asynchronous transport, you will need to wait till it is written before exiting the program


Help us improve and be recognised!

Aleš Menzel

💻 📖

This project follows the all-contributors specification. Contributions of any kind are welcome!


This package is developed under the MIT licence.