JSON Log

Easy to use logger that prints stuff in a json format for log ingestion.

Exports

createLogger(minLevel, ctx, ...targets)

Creates a logger with any number of log targets and default context.

logLevel

An object with numeric values for the various log levels. (I use this to configure log level using env vars cause I'm lazy) Levels:

• debug

  Allow all logs

• info

  Don't log debug messages

• warn

  Don't log debug, info

• error

  Only log error messages

• none

  Turn off logging without removing every function call in the code

basic

A log target that just logs the message as is, with a timestamp added to it.

datadog

A log target that prints the log and its context as a JSON string on a single line so that the default Datadog JSON parsing can be used to process the logs without any kind of special config.

object

A log target that shows the log message, timestamp, level, and context as an object printed in the console.

default export

The default export of the library is the built in basic logger. See the API section for details.

API

The API for logging is based on creating loggers, or using any of the built in logger provided by the library. Each of the built in targets also has a default logger on the .logger property that is configured to allow all logs with an empty initial context and uses only that target (ex: basic.logger).

Logger.debug(message, context)

Logs a message and the additional context at the DEBUG level

Logger.info(message, context)

Logs a message and the additional context at the INFO level

Logger.warn(message, context)

Logs a message and the additional context at the WARN level

Logger.error(message, context)

Logs a message and the additional context at the ERROR level

Logger.child and Child Loggers

The Logger.child(extraCtx, newMinLevel?) can be used to create child loggers. A child logger inherits the context and log level of its parent unless a new min log level is given, and merges the extraCtx with the parents context to create its own. There is no limit to the depth of children.

const parent = createLogger(logLevel.debug, { id: 1 }, object)
const child = parent.child({ isChild: true }, logLevel.info)

// logs with the context { id: 1 }
parent.debug("test")
// logs with the context { id: 1, isChild: true }
child.info("test")
// won't log anything
child.debug("test")

Example

See the examples folder in the repo.