A dead simple logger, designed to be perfect for the browser.

• No configuration necessary—with sane defaults based on your NODE_ENV and LOG_LEVEL variables.
• Makes your logging nice and easy to read in development.
• Only logs errors by default in production, so user's won't see junk in the console.
• Leverages the browser's smart, built-in console formatting and stack traces.

Given an API which is what you'd expect...

import logger from 'browser-logger'

logger.info('Websocket connected!', { port: 4000 })
logger.error('Invalid `type` argument', { argument: 'type', value: 'nuber' })

In development, it outputs an easy to read version, using the browser's built-in formatting...

And in production it will only log errors by default, to not confuse users who might open the console.

That's it!

The default console behavior in most browsers these days has a nice API, with great support for different data types and stack traces. But things get noisey without some control over the "log level".

Unfortunately most of the browser-focused logging libraries aren't great—they're bloated in size, or they use console.log which doesn't add stack traces for errors, or they're overly complex to setup.

I wanted a super-simple logger for the browser, with sane defaults.

That way you can just import 'browser-logger' and not have to worry about configuring things at all.

import logger from 'browser-logger'

logger.info('message', { key: 'value' })

[info] message  { key: 'value' }

The package exports the one-liner logger singleton as the default, which is already instanciated with sane defaults using the NODE_ENV environment variable and the LOG_LEVEL Local Storage variable.

localStorage.setItem('LOG_LEVEL', 'warn')

To change the level of logs that are output, set the Local Storage LOG_LEVEL variable. (Or you can do it via your browser's developer tools UI.)

If you want to completely disable logging, set LOG_LEVEL to 'none'.

import { Logger } from 'browser-logger'

const logger = new Logger({
  level: String,     // Defaults to `LOG_LEVEL` if set, or `'info'`.
  prefix: String,    // Defaults to `''`.
})

If you need to create multiple instances, which can be useful for subclassing loggers based on the parts of your system, the Logger constructor is also exported, which takes the following options:

• level sets the current log threshold, silencing logs that don't meet it.
• prefix sets a string that will be prepend to every message.

logger.info('message', { key: 'value' })
logger.error('error!', { code: 400 })

[info] message  { key: 'value' }
[error] error!  { code: 400 }

Log a message with data to the console at level, where level is one of:

• trace
• debug
• info
• warn
• error
• fatal

You can also pass an Error object as a message, in which case the logger will automatically convert it into useful message and data with a full stack trace.

logger.log('info', 'message', { key: 'value' })

[info] message  { key: 'value' }

Log a message with data to the console at level.

const other = logger.clone({ prefix: '[package] ' })

other.info('message', { key: 'value' })

[info] [package] message  { key: 'value' }

Create a new Logger instance, copying the existing loggers config, but extending it with optional options.