Irrelon Log

A simple console logging module.

Install

npm i irrelon-log

Usage

const {init} = require('./index');
const log = init('Demo File', '1.0.1');

log.info('Testing how a log line looks');

// Output is:
// 2019-06-04 18:01:09 (28563) [1.0.1] [DEBUG] *Demo File* Testing how a debug line looks

Defaults

Irrelon Log sets some default levels for log lines. The module determines if you are in dev or production by the NODE_ENV environment variable value.

The defaults are:

• debug: off
• info: on in "dev", off in "production"
• warn: on in "dev", off in "production"
• error: on

Overriding Defaults

You can override default log levels in a number of ways either in code or using environment variables. The environment variable option provides a very thorough way to control logs at both a global level (the entire application) and a module level (you can set levels targeted at a module's name which will override any levels specified in code).

Env Var Language

When setting the value of a log level, you can use the log level name to set to true / on or use an exclamation mark and then the log level name to set to false / off. E.g. "debug" (on) vs "!debug" (off).

Examples of Environment Variable Settings

All Logs Enabled

IRRELON_LOG=*

All Logs Disabled

IRRELON_LOG=!*

All Logs Enabled Except Debug

IRRELON_LOG=*,!debug

All Logs Disabled Except Debug

IRRELON_LOG=!*,debug

Module Level Environment Variable Settings

Imagine we have an application with many different modules. In each module we wish to have log output we require or import Irrelon Log and then setup a "log" constant to use:

const {version} = require("./package"); // Read package.json for version
const {init} = require("irrelon-log");
const log = init("Module1", version);

Now imagine we have Module2, Module3 and so on.

During debugging we might want to control output so we silence all other modules except Module2 and silence all Module2 log levels EXCEPT "debug".

We can achieve this and many other scenarios like so:

All Logs Disabled But Override "Module2" debug to Enabled

IRRELON_LOG=!*,Module2=debug

All Logs Enabled But Override "Module2" debug to Disabled

IRRELON_LOG=*,Module2=!debug

All Logs Enabled But Override Multiple Module Levels

IRRELON_LOG=*,Module1=info,Module1=error,Module2=!debug

Code-Based Level Settings / Overrides

At a module level you can set log level settings when calling init().

const {version} = require("./package"); // Read package.json for version
const {init} = require("irrelon-log");
const log = init("Module1", version, {
	debug: true,
	info: false,
	warn: true,
	error: false
});

Log Level Priority

Irrelon Log uses a priority order to determine if a log line should be output or not. That priority order looks like this:

1. Module Level Environment Variable Value
2. Module Level Code Value
3. Global Level Environment Variable Value
4. Irrelon Log Default Value

If a value is found in (1) then we don't check (2) for a value and so on. In other words the list above is from highest priority to lowest.

Methods

All methods eventually call a console.* method using built-in console capability. The bit Irrelon Log does is add a bunch of extra info on each call like the process id, date/time, application name and version.

All arguments sent to one of these methods is passed to the console call so you can add as many args as you like.

debug (msg[,...])

Output a debug message via console.log(). This is different from info() in that debug() should be used for development purposes or when you are writing a module and want debug output that module consumers can switch on or off. Debug logs are disabled by default so module consumers must explicitly enable them to see debug output.

const obj = {foo: true};
log.info('Some object output', obj, "foo", "bar", 1, 2, 4);

info (msg[,...])

Output an info message via console.log().

const obj = {foo: true};
log.info('Some object output', obj);

warn (msg[,...])

Output a warning via console.warn().

const obj = {foo: true};
log.warn('Some object output', obj);

error (msg[,...])

Output an error via console.error().

const obj = {foo: true};
log.error('Some object output', obj);