@seald-io/logger

@seald-io/logger is a logger packages, which pretty-prints logs to the console, and allows to change log-levels and export the log history.

You can use the default export (usually named makeLogger), to create a logger instance.

A logger instance contains 4 logging functions with varying levels, debug, info, warn, error.

By default, debug-level logs are hidden, anything superior is shown.

Usage

import makeLogger from '@seald-io/logger'

const logger = makeLogger('my-app')

logger.info('this is an info message, it will print by default')
logger.debug('this is a debug message, it will *not* print by default')

Changing log level

Concept

The default log level is *:info. This means that all namespaces (*) print levels info and up.

You can use the function setLogLevel to change this log level.

import makeLogger, {setLogLevel} from '@seald-io/logger'

const logger = makeLogger('my-app')

logger.debug('this is a debug message, it will *not* print')

setLogLevel('*:debug') // this sets all namespaces to print all logs

logger.debug('this is a debug message, but it will print because log level was changed')

Namespaces

You can also change log levels only for a specific namespace.

import makeLogger, {setLogLevel} from '@seald-io/logger'

const logger1 = makeLogger('logger1')
const logger2 = makeLogger('logger2')

setLogLevel('logger1:debug') // logger1 will now print debug messages

logger1.debug('this is a debug message, but it will print because log level was changed for this logger')

logger2.debug('this is a debug message, but it will *not* print because it is in another namespace')

Warning, this actually overrides the default log level, so anything other than logger1 will now not print at all, even for higher levels!

If you want to still print info messages, you can do instead:

setLogLevel('logger1:debug,*:info') // logger1 will now print debug messages, other loggers will print info

You can also provide multiple namespaces, separated by ,.

setLogLevel('logger1:debug,logger2:info,*:error') // logger1 will now print debug messages, logger1 will print info, other loggers will only print errors

You can also use environment variables to set the log level, instead of calling setLogLevel in your code. @seald-io/logger can be configured with the following environment variables (by order of priority):

• LOG_LEVEL
• DEBUG_NAMESPACES
• DEBUG

The syntax for environment variables is the same, except that it always keeps the default *:info level in addition to the ones you specify.

You may want to run setLogLevel as soon as possible after your app has started, to see startup messages. A "trick" to run it as soon as possible is to have it in a separate file which is then imported into your main file.

History

@seald-io/logger keeps a history of the logged messages, which you may subsequently export.

The setHistorySize function allows you to set the number of messages saved to this history. It defaults to 10,000 lines.

The flushToString function exports the current history to a string.