@jsenv/logger

Logger

Control verbosity of logs during a function execution.

Table of contents

• Presentation
• Usage
  • createLogger
  • logLevel
  • logger
  • Migration from console
• Installation

Presentation

You want to use @jsenv/logger when you have many logs with different purposes and controls which type of logs are actually written.

jsenv-logger github repository corresponds to @jsenv/logger package published on github and npm package registries.

Usage

This documentation explains how to use @jsenv/logger in your codebase.

createLogger

createLogger is a function receiving a logLevel and returning a logger object.

Implemented in src/createLogger.js, you can use it as shown below.

import { createLogger } from "@jsenv/logger"

const functionWithLogs = ({ logLevel }) => {
  const logger = createLogger({ logLevel })

  logger.debug("start doing whetevr")
  logger.info("some useful info")
  logger.debug("doing whatever is done")
  logger.warn("be careful about blah-blah")
  logger.error("oops an error occured while doing whatever")
}

functionWithLogs({ logLevel: "debug" })
functionWithLogs({ logLevel: "info" })
functionWithLogs({ logLevel: "warn" })
functionWithLogs({ logLevel: "error" })
functionWithLogs({ logLevel: "off" })

logLevel

logLevel parameter is a string controlling verbosity of the returned logger.

The possible logLevel values are:

• "off"
• "debug"
• "info"
• "warn"
• "error"

If you are rigorous, each logLevel value is exported as a constant that you can use like this:

import { createLogger, LOG_LEVEL_INFO } from "@jsenv/logger"

createLogger({ logLevel: LOG_LEVEL_INFO })

logger

logger is an object with methods logging a message with a given level.

It is returned by createLogger, and has the following shape: { debug, info, warn, error }. Each method calls the corresponding console method or do nothing depending on the logLevel.

import { createLogger } from "@jsenv/logger"

const logger = createLogger({ logLevel: "info" })
logger.debug("hello")

Logs nothing

import { createLogger } from "@jsenv/logger"

const logger = createLogger({ logLevel: "info" })
logger.info("hello")

Logs Hello

Migration from console

Using @jsenv/logger means converting console methods into logger methods. console.info becomes logger.info and so on.

But keep in mind there is no logger.log. This is because a log level named "log" would not fit into the log level hierachy below.

error > warn > info > debug

It means you have to convert console.log into logger.debug or logger.info.

Installation

Before installing, please note that you cannot directly require this package because there is no commonjs version for the source code.

If you never installed a jsenv package, read Installing a jsenv package before going further.

This documentation is up-to-date with a specific version so prefer any of the following commands

npm install @jsenv/logger@3.2.0

yarn add @jsenv/logger@3.2.0