slf4n-logging

Simple Logging Facade for NodeJS

Emulating Simple Logging Facade for Java (SLF4J)

!ss

This shiz is asynchronous!

Yes, logger functions' implementation for writing to streams won't be a blocker.

Every log method returns a bluebird Promise -- for those that want to "wait" for logs to be written before proceding to next lines.

_slf4n-logging by jpbaking_

How to use?

$3

Simply require('slf4n-logging') from your "main" (entrypoint) .js then all of other modules would get the global LoggerFactory.

Sample File #1: app.js
``javascript
require('slf4n-logging');
`

Sample File #2: api/controller/health.js
`javascript
const log = LoggerFactory.getLogger('app:health');
// ...
log.debug('some debug line %s', aStringVariable);
log.debug('some debug line %o', anObjectOrArray);
// ...
log.error('some error line', error);
`

#### Formatting in log.{level}([data][, ...args])

As shown in the example above, syntax for log-level functions exactly the same as [require('util').format(format[, ...args])](https://nodejs.org/api/util.html#util_util_format_format_args) and [console.log([data][, ...args])](https://nodejs.org/api/console.html#console_console_log_data_args).

$3

Some do not like adding anything to global.*. If you're one of those, you may use require('slf4n-logging/safe') instead:

Sample File: api/helpers/UltimateHelper.js
`javascript
const log = require('slf4n-logging/safe')('app:ultimate');
// ...
log.info('some info line');
// ...
log.warn('some warn line', error);
`

$3

Sample loggerConfig object:
`javascript
// example
const loggerConfig = {
layout: '[:level] :timestamp :logger - :message:error',
errorIndenter: ' > ',
level: 'trace',
colors: {
enabled: 'true',
fatal: 'magenta',
error: 'red',
warn: 'yellow',
info: 'white',
debug: 'cyan',
trace: 'green'
},
stream: 'stderr',
terminateOnFail: 'true'
}
`

Sample global.LoggerFactory _(unsafe)_:
`javascript
// logger factory
// unsafe usage (global.LoggerFactory is set)
require('slf4n-logging/json')(loggerConfig, false);
// default is false for safe (second argument)
require('slf4n-logging/json')(loggerConfig);

// actual logger
const log = LoggerFactory.getLogger('app:something');
// ...
log.debug('some debug line');
// ...
log.error('some error line', error);
`

Sample safe usage _(returns a LoggerFactory; same one that would've been set to global.*)_:
`javascript
// logger factory
const LoggerFactory = require('slf4n-logging/json')(loggerConfig, true);

// actual logger
const log = LoggerFactory.getLogger('app:something');
// ...
log.trace('some trace line');
// ...
log.fatal('some fatal line', error);
`

The log.{level}([data][, ...args]) functions

As described earlier, just use log.{level}([data][, ...args]) functions very much like how you'd use [console.log([data][, ...args])](https://nodejs.org/api/console.html#console_console_log_data_args).

`javascript
const log = LoggerFactory.getLogger('app:something');
// ...
try {
log.trace('something trace %s', aString);
log.debug('something debug %o', anObject);
log.info('something info');
log.warn('something warn %d', aNumber);
// ...
} catch (error) {
log.fatal('something fatal', error);
log.error('something error', error);
}
`

Here's a list of available log.{level}([data][, ...args]) functions:

- log.fatal([data][, ...args]) - log something at fatal level
- log.error([data][, ...args]) - log something at error level
- log.warn([data][, ...args]) - log something at warn level
- log.info([data][, ...args]) - log something at info level
- log.debug([data][, ...args]) - log something at debug level
- log.trace([data][, ...args]) - log something at trace level

The log.is{level}Enabled() function

Intended string/s to log are expensive to generate outside of util.format()? Check if level can be logged in the first place!!!

`javascript
const log = LoggerFactory.getLogger('app:something');
// ...
if (log.isTraceEnabled()) {
log.trace('Stats:\n%s', someHeavyStatistics.snapshot().prettyPrint());
}
`

In the example above, #snapshot() and/or #prettyPrint() is expensive to execute; hence, checking if the log level is enabled first.

- #isFatalEnabled() - check if fatal is enabled
- #isErrorEnabled() - check if error is enabled
- #isWarnEnabled() - check if warn is enabled
- #isInfoEnabled() - check if info is enabled
- #isDebugEnabled() - check if debug is enabled
- #isTraceEnabled() - check if trace is enabled

Configuration

$3

Here are the environment variables that can be set to configure slf4n-logging:

#### LOG_LAYOUT

> "Manual" Usage JSON Path: .layout

The layout / pattern for every log line written.

> :timestamp [:level] :logger@:hostname (:pid) - :message:error

Placeholders:
- :timestamp - is replaced by ISO8601 date string _(ie.: 2018-06-17T10:38:19.336Z)_
- :level - the level or verbosity of logs allowed to be written
- :logger - the loggerName
- :hostname - the machine hostname from where app is running
- :pid - the process ID (PID) of running app
- :message - the message to be logged
- :error - to show/print error and/or error.stack
- :[n] - new-line

Color placeholders:

| FORMATS | FOREGROUND | BACKGROUND |
| ---------------- | ---------------- | ---------------- |
| :c[reset] | :c[black] | :c[bg.black] |
| :c[bold] | :c[red] | :c[bg.red] |
| :c[dim] | :c[green] | :c[bg.green] |
| :c[underscore] | :c[yellow] | :c[bg.yellow] |
| :c[blink] | :c[blue] | :c[bg.blue] |
| :c[reverse] | :c[magenta] | :c[bg.magenta] |
| :c[hidden] | :c[cyan] | :c[bg.cyan] |
| | :c[white] | :c[bg.white] |

How to color? Here's a sample:

> :c[bold]:c[level][:level]:c[reset] :logger - :message:c[level]:error

It'll look like:

!ss_coloring.png

#### LOG_LEVEL

> "Manual" Usage JSON Path: .level

The "max" level or verbosity of logs allowed to be written. Better explained by the list of accepted values below:

- OFF - nothing will be printed
- FATAL - only level FATAL will be printed
- ERROR - levels ERROR, FATAL, will be printed
- WARN - levels WARN, ERROR, FATAL, will be printed
- INFO - levels INFO, WARN, ERROR, FATAL, will be printed
- DEBUG - levels DEBUG, INFO, WARN, ERROR, FATAL, will be printed
- TRACE - levels TRACE, DEBUG, INFO, WARN, ERROR, FATAL, will be printed

Default is INFO if left unset.

#### LOG_COLORS_ENABLED

> "Manual" Usage JSON Path: .colors.enabled

To enable/disable colors in logging. Note that setting this to true will NOT override printing colors over non-TTY terminals/consoles/streams _(if stream is NOT TTY, colors won't be printed)_.

- true - colors (:c[*]) will be printed
- false - no color will be printed

Default is true if left unset.

#### LOG_COLORS_{level}

> "Manual" Usage JSON Path: .colors.{level_in_lowercase}
> - .colors.fatal
> - .colors.error
> - .colors.warn
> - .colors.info
> - .colors.debug
> - .colors.trace

- LOG_COLORS_FATAL - color to be used for FATAL level logs _(default: magenta)_
- LOG_COLORS_ERROR - color to be used for ERROR level logs _(default: red)_
- LOG_COLORS_WARN - color to be used for WARN level logs _(default: yellow)_
- LOG_COLORS_INFO - color to be used for INFO level logs _(default: white)_
- LOG_COLORS_DEBUG - color to be used for DEBUG level logs _(default: green)_
- LOG_COLORS_TRACE - color to be used for TRACE level logs _(default: cyan)_

Here are the valid colors:

| FORMATS | FOREGROUND | BACKGROUND |
| ---------- | ---------- | ---------- |
| reset | black | bg.black |
| bold | red | bg.red |
| dim | green | bg.green |
| underscore | yellow | bg.yellow |
| blink | blue | bg.blue |
| reverse | magenta | bg.magenta |
| hidden | cyan | bg.cyan |
| | white | bg.white |

#### LOG_ERROR_INDENTER

> "Manual" Usage JSON Path: .errorIndenter

Used to indent error stack. " | " _(the default; four spaces, a pipe, then a space)_ would appear like:

![](./.readme/ss_indenter.png)

Not really necessary, sure there's overhead, but does look nice :P _(improves readability for some)_

#### LOG_STREAM

> "Manual" Usage JSON Path: .stream

Dictates which stream (stdout and/or stderr) to route log writing.

| LOG_STREAM | "out" | "err" |
| -------------- | ---------------- | ---------------- |
| DEFAULT | process.stdout | process.stdout |
| STDOUT | process.stdout | process.stdout |
| STDERR | process.stderr | process.stderr |
| STANDARD | process.stdout | process.stderr |

> FATAL and ERROR are logged to "err" streams.
>
> WARN, INFO, DEBUG, and TRACE, are logged to "out" streams.

#### LOG_TERMINATE_ON_FAIL

> "Manual" Usage JSON Path: .terminateOnFail

Basically, whether or not to terminate running app if writing logs into stream fails.

- true - colors (:c[*]) will be printed
- false - no color will be printed

Default is true` if left unset.

License

MIT License

Copyright (c) 2018 Joseph Baking

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.