@jsenv/logger

logger

Control verbosity of logs during a function execution.

Table of contents

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

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.

Installation

npm install @jsenv/logger@3.3.1

Documentation

createLogger

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

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" })

— source code at src/createLogger.js.

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.