Simple universal and extra-light (1kB) logger for node/browser, with prefix, time and colours.





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Simple logger

Simple universal and extra-light (1kB) logger for node/browser, with prefix, time and colours.

This simple utility is <1kB and is optimised to disable all logging in production, display log time, line of origin, prefix and sane colors on the server console.

Also, it is tree-shacked and has the same API as the console native object.

We use it with Next.js and Vercel, and we don't need the server logs on production because we have Sentry for that, and disabling them reduces our cost.


import createSimpleLogger from '@unly/simple-logger';

const logger = createSimpleLogger({
  prefix: 'My lib',
  shouldPrint: () => process.env.NODE_ENV !== 'production', // Only print in non-production env (default behavior)

Make sure to check our advanced examples below!

Example color output (server console)


This is an example of the default color behaviour (see scripts/show-colors.js).

We recommend adapting:

  • The prefix option, using the filename, the class name, the module name, etc. to help locate the origin of the message.
  • The shouldPrint option to your needs. By default, it won't print anything in production environment.
  • The colorize option, if you want to customize the colors used on the server. See colorizeFallback for inspiration.


yarn add @unly/simple-logger


npm install @unly/simple-logger

Peer dependencies

You'll also need to install those peer dependencies:

  • yarn add chalk

We decided to allow you to decide what version of chalk you want to use for greater flexibility.


Here are a few options to adapt the lib to your own needs.

export type SimpleLoggerOptions = {
  prefix?: string;
  disableAutoWrapPrefix?: boolean;
  colorize?: Colorize;
  shouldPrint?: ShouldPrint;
  shouldShowTime?: ShouldShowTime;
  timeFormat?: TimeFormat;

export type Colorize = (mode: PrintMode, prefixes: string[]) => string[];
export type ShouldPrint = (mode: PrintMode) => boolean;
export type ShouldShowTime = () => boolean;
export type TimeFormat = () => string;

Default options

prefix: None
disableAutoWrapPrefix: `false`
colorize: Colorize for server console only, see implementation
shouldPrint: Prints if NODE_ENV !== 'production'
shouldShowTime: Enabled
timeFormat: Using ISO string

Advanced configuration

You can define the following environment variables:

  • UNLY_SIMPLE_LOGGER_ENV: Will be used instead of NODE_ENV, to configure the default behavior of shouldPrint.
    • E.g: If set to APP_STAGE, then will compare APP_STAGE with production. If APP_STAGE = 'staging' (or development), then shouldPrint will print by default. If APP_STAGE = 'production', then shouldPrint will not print by default. If a custom shouldPrint is provided, then it will ignore UNLY_SIMPLE_LOGGER_ENV as it won't rely on the default shouldPrint implementation.
  • SIMPLE_LOGGER_SHOULD_SHOW_TIME: Will be used to configure whether to show the time by default.
    • E.g: If set to false, then will not show the time.

Advanced examples

Those advanced examples are taken from actual implementation in production-grade applications.

Application-wide logger

If you want to define your config only once and reuse it everywhere across your app, you can write a proxy, see below:


import createSimpleLogger, { SimpleLogger } from '@unly/simple-logger';

 * Custom logger proxy.
 * Customize the @unly/simple-logger library by providing app-wide default behavior.
 * @param fileLabel
export const createLogger = ({ fileLabel }: { fileLabel: string }): SimpleLogger => {
  return createSimpleLogger({
    prefix: fileLabel,
    shouldPrint: (mode) => {
      return process.env.NEXT_PUBLIC_APP_STAGE !== 'production';


import { createLogger } from '../logger';

const fileLabel = 'someFile';
const logger = createLogger({

logger.warn(`Oops, a warning!`, { x: 1 })

Silent all logs during tests (Jest)

Similar to the previous example, the createLogger can be used to change the behaviors for tests.

In the below example, the NODE_ENV equals test during tests (when running yarn test) and it makes it easy to change the behavior to use console instead of the logger in such case. Combined with other configuration, it allows to silent all logs when using either console or logger during tests.


 * Custom logger proxy.
 * Customize the @unly/simple-logger library by providing app-wide default behavior.
 * @param fileLabel
export const createLogger = ({ fileLabel }: { fileLabel: string }): SimpleLogger => {
    // Mute logger during tests, to avoid cluttering the console
    if (process.env.NODE_ENV === 'test') {
      return global.muteConsole();

    return createSimpleLogger({
      prefix: fileLabel,
      shouldPrint: (mode) => {
        return process.env.NEXT_PUBLIC_APP_STAGE !== 'production';


We gladly accept PRs, but please open an issue first, so we can discuss it beforehand.


No changelog for now. WIP. Thinking of using https://github.com/semantic-release/semantic-release.

Releases versioning

We follow Semantic Versioning. (major.minor.patch)



Vulnerability disclosure

See our policy.

Contributors and maintainers

This project is being authored by:

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