@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:

`ts
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:

`ts
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
`

$3

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

$3

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

Example:

`ts
// 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
`

$3

File name usage:

`ts
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
`

$3

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:

`ts
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