Sift Logger

Usage no npm install needed!

<script type="module">
  import siftLogger from 'https://cdn.skypack.dev/@sift/logger';



Log Levels

  • CRIT - A critical error has occured, and the process has crashed.
  • ERROR - An unexpected error has occured, and the process may have crashed.
  • WARNING - An issue has occurred that warrants notification, but the process was allowed to continue.
  • INFO - An informational message that should be displayed in production.
  • DEBUG - A message that should only be displayed during development.

Logs at INFO or greater severity will be logged by default.

Retrieving a Logger

get-logger will retrieve an existing logger if a logger has already been created for the given module name, otherwise, a new logger with default options will be created automatically and returned.


import { getLogger } from '@sift/logger';

const logger = getLogger('modulea');

logger.info('Hello World!');

Building a Logger

build-logger will create a new logger if no logger exists for the given module name, otherwise the existing cached logger will be overridden. Currently, loggers that have already been retrieved from the cache will not be updated when build-logger is called for an existing module.

build-logger Configuration

  • moduleName (required) - The moduleName that will be used as the logger cache key. This value will also be included with all logs.
  • parent (optional) - A parent logger that the new logger will inherit options from.
  • options (optional) - Optional logger configuration. Any options specified will override options from the parent.
  • options.level - The maximum level to log at (see Log Levels).


import {
} from '@sift/logger';

const parentLogger = buildLogger({
  moduleName: 'parent',
  options: {
    level: Level.DEBUG,

const logger = buildLogger({
  parent: parentLogger,
  moduleName: 'logger',

Building a Request Logger

build-request-logger will create a new logger middleware designed to be used with Express. This logger is primarily for logging HTTP traffic passing through the Express app.

build-request-logger Configuration

  • logger (required) - The logger to use when logging within the middleware
  • appName (required) - The name of the application, usually the name within package.json
  • logRequestImmediately (optional) - Whether or not a request should be logged immediately before the response is returned. This option makes sure requests are logged, even if the server crashes; however, the response will not be included in the log.

Structuring Loggers

It is recommended that a root logger is created for the entire application, and loggers are created for each major module in the application. The root logger will serve as the parent for each major module. Each file in the module will use the module logger.


Root Logger


import { buildLogger } from '@sift/logger';

export default buildLogger({
  moduleName: 'project',

Module Logger


import { buildLogger } from '@sift/logger';
import rootLogger from '../logger';

export default buildLogger({
  parent: rootLogger,
  moduleName: 'project.modulea',

Module File


import logger from './logger';

logger.info('hello world!');



import {
} from '@sift/logger';

const logger = getLogger('module');
logger.log(Level.INFO, 'Hello world!');

{"timestamp":"2019-04-05T15:17:39.951Z","level":"INFO","module":"module","message":"Hello world!"}


import { getLogger } from '@sift/logger';

const logger = getLogger('module');
logger.crit('Hello world!');

{"timestamp":"2019-04-05T15:14:29.384Z","level":"CRIT","module":"module","message":"Hello world!"}


import { getLogger } from '@sift/logger';

const logger = getLogger('module');
logger.error('Hello world!');

{"timestamp":"2019-04-05T15:14:11.545Z","level":"ERROR","module":"module","message":"Hello world!"}


import { getLogger } from '@sift/logger';

const logger = getLogger('module');
logger.warning('Hello world!');

{"timestamp":"2019-04-05T15:13:22.852Z","level":"WARNING","module":"module","message":"Hello world!"}


import { getLogger } from '@sift/logger';

const logger = getLogger('module');
logger.info('Hello world!');

{"timestamp":"2019-04-05T15:13:03.391Z","level":"INFO","module":"module","message":"Hello world!"}


import { getLogger } from '@sift/logger';

const logger = getLogger('module');
logger.debug('Hello world!');

{"timestamp":"2019-04-05T15:12:36.264Z","level":"DEBUG","module":"module","message":"Hello world!"}

Exception Logging

When an Exception is logged, The message will be extracted from the Exception, and the Exception's stacktrace will be included as stack.

import { getLogger } from '@sift/logger';

const logger = getLogger('module');
logger.warning(new Error('Hello Error!'));

{"timestamp":"2019-04-05T15:07:48.291Z","level":"WARNING","module":"module","message":"Hello Error!","stack":"Error: Hello Error!\n at Object.<anonymous> (/home/tnewman/repos/Lib.Core/test.js:5:16)\n at Module._compile (module.js:653:30)\n at Object.Module._extensions..js (module.js:664:10)\n at Module.load (module.js:566:32)\n at tryModuleLoad (module.js:506:12)\n at Function.Module._load (module.js:498:3)\n at Function.Module.runMain (module.js:694:10)\n at startup (bootstrap_node.js:204:16)\n at bootstrap_node.js:625:3"}

Message Type

Includes the messageType field in the log to make it easy to identify standardized messages, such as requests.

import { getLogger } from '@sift/logger';

const logger = getLogger('module');
logger.info('Hello World!', { messageType: 'string' });

{"timestamp":"2019-04-05T15:06:34.642Z","level":"INFO","module":"module","messageType":"string","message":"Hello World!"}

LOG_LEVEL Environment Variable

Setting the LOG_LEVEL environment variable will override the log level for every logger.

LOG_LEVEL=debug node test.js