@arpinum/log

We are drowning in information but starved for knowledge.
John Naisbitt

@arpinum/log is a simple module to log on stdout or stderr.

Installation

npm install @arpinum/log --save

Default logger

Just import default logger and start yelling messages:

import { logger } from "@arpinum/log";

logger.info("Something happened");

Which outputs :

2017-01-30T09:15:04.821Z - info: [default] Something happened

Logging methods

Available methods are:

• debug
• info
• warn
• error

Each level uses corresponding method on console global object and fallback to console.log if missing for runtime environment.

Custom logger

You can create a fine tuned logger:

import { createLogger } from "@arpinum/log";

const logger = createLogger({ level: "error" });
logger.info("Something happened");
logger.error("Some error");

Which outputs :

2017-01-30T09:23:33.417Z - error: [default] Some error

Options

You can pass those options during logger creation:

• level
  • minimum logging level amongst all, debug, info, warn, error, off
  • default is info
  • ARP_LOG_LEVEL env var may be used to set level
• category
  • the category displayed in message, useful to filter logs
  • default is default
• fileName
  • a category can be created from a base name without extension of a file
• filter
  • a regex to filter matching categories
  • default is .* (open bar)
  • ARP_LOG_FILTER env var may be used to set filter
• getDateString
  • a function to get a formatted date
  • default function returns new Date().toISOString()
  • provide null if you do not want a date at all
• getLogInputs
  • a function to get inputs given to console methods
  • used to format message as you want
  • see Customize message below

Filtering logs

If you have multiple logger instances with various categories, you can filter logs using filter options or ARP_LOG_FILTER env var.

Example:

// program.js
const mainLogger = createLogger({ category: "main" });
const serviceLogger = createLogger({ category: "service" });

mainLogger.info("Application started");
serviceLogger.info("Doing some stuff");

May be run with LOG_FILTER=serv node program.js to output:

2017-01-30T09:32:31.351Z - info: [service] Doing some stuff

About category:

File name usage:

import { createLogger } from "@arpinum/log";

const logger = createLogger({ fileName: __filename });
logger.info("Something happened");

Which outputs :

2017-01-30T09:32:31.351Z - info: [MySuperClass] Something happened

Customize message

getLogInputs will be called for each log with an object containing:

• date: the current date string
• category: the configured category
• level: the logger level
• args: all the provided args

Example:

const logger = createLogger({
  getLogInputs: ({ date, category, level, args }) => [
    `${date}|${category}|${level}`,
    ...args,
  ],
});

logger.info("My", "message");

// 2019-11-19T16:45:58.419Z|default|info My message

License

MIT