@bebrasmell/mono-logger

Mono-logger

A simple logger module with topics and side-effects capabilities. It comes pretty useful when need to share common loggers across multiple modules or to nest loggers with different topics (e.g. function executors for debugging purposes).

Default logs format:

7/26/2024, 20:54:26 [DBG] hello, world

Changelog

Please see CHANGELOG for latest changes.

Installation

yarn add @bebrasmell/mono-logger

Or

npm i @bebrasmell/mono-logger

Topics

You can create a new child logger with a specific topic. This way you can filter logs by topic.

import { Logger } from '@bebrasmell/mono-logger';

const logger = new Logger();
const subLogger = logger.topic('sub-topic');
const deepSubLogger = subLogger.topic('deep-sub-topic');

deepSubLogger.log('hello, world');

// Output:
// 7/26/2024, 21:11:09 [DBG] sub-topic:deep-sub-topic hello, world

You can also access parent logger from a child logger.

import { Logger } from '@bebrasmell/mono-logger';

const logger = new Logger();
const subLogger = logger.topic('sub-topic');
const deepSubLogger = subLogger.topic('deep-sub-topic');

deepSubLogger._parent?.log('hello, world');

// Output:
// 7/26/2024, 21:11:09 [DBG] sub-topic hello, world

Configuration

Configuration can be set for the root logger or specific topic and its descendants. It means, that topic configuration will be inherited from it's parent. When you provide options for a new topic, it's going to override its parent configuration entirely.

Example:

const root_logger = new Logger("root", {
    level: "info",
});

const sub_logger = root_logger.topic("leaf", {});

sub_logger.debug("I am still here!");
// Output:
// 7/26/2024, 21:11:09 [DBG] root:leaf I am still here!

You can configure the logger with:

• level: (e.g. debug) The minimum log level to be displayed.
• prefix: (function) A prefix to be added to each log record before topics.
• date_format: (function) The date formatter function to be used in logs.
• effect: (function) A side-effect function to be called on each log record. It receives log level, list of topics and spread raw data array passed to logger.
• transform: (function) A function to transform log records before being displayed.
• force_effect: (boolean) If true, side-effects will be called even if log level is below the minimum level.

import { Logger } from '@bebrasmell/mono-logger';

const ex_logger = new Logger('example', {
  level: 'debug',
  prefix: () => 'my-app',
  date_format: (date) => date.toISOString(),
  effect: (level, topics, ...data) => console.log(level, topics, ...data),
  transform: (m) => `yes, ${m}`,
  force_effect: true,
});

ex_logger.log('hello', 'world');

// Output:
// 2024-07-26T18:47:01.978Z [DBG] my-app example yes, hello yes, world
// debug [ 'example' ] hello world

Side effects

You can assign any side effect you want to any topic and it's descendants (see Configuration). So each time you log something, the logger fires the effect function with parameters:

• level - log level
• topics (array, root to leaf)
• ...raw data you passed to logger

By default, when you log something below the minimum log level specified in Topic Configuration, effect is not fired. You can force logger to fire it by passing force_effect.

Inheritance

By default, every child logger will inherit configuration from it's parent, but if you'd like to customize a specific parameter, you can access parent's configuration as a readonly object:

const parent = logger.topic("parent", {
  /* ... */
});

const child = root.topic("child", {
  ...parent._config,
  effect: () => { /* do something else */ },
});

![note] You should not modify or override existing configuration. That is done on purpose to preserve verbosity and functional consistency.

MonoEffects and PolyEffects

MonoEffect is a wrapper around your effect function with minimum log level check. Imagine this:

• Some module has a topic that is logged with info level;
• There's a need to explicitly process all the warn, error and fatal logs that are generated by the module;
• You create an effect and attach it to the topic logger;

In such situations, you can use MonoEffect:

import { MonoEffect } from "@bebrasmell/mono-logger";

const handleWarnings = (lvl, topics, ...messages) => {
  /*
   * ...
   * your custom warn, error and fatal handler
   * ...
   */
  console.warn("Warning has been recorded and saved");
};

const warnings_effect = new MonoEffect(handleWarnings, "warn");

const logger = root_logger.topic("target_module_name", {
  level: "info",
  effect: warnings_effect,
});

logger.warn("Example warning");

// Output:
// 2024-07-26T18:47:01.978Z [WRN] target_module_name Example warning
// Warning has been recorded and saved

PolyEffect simply concatenates your effects and fires them one after another.

import { MonoEffect, PolyEffect } from "@bebrasmell/mono-logger";

const handleWarnings = (lvl, topics, ...messages) => {
  /*
   * ...
   * your custom warn, error and fatal handler
   * ...
   */
  console.warn("Warning has been recorded and saved");
};

const handleFatal = (lvl, topics, ...messages) => {
  /*
   * ...
   * your custom fatal handler
   * ...
   */
  console.error("x_x");
};

const warnings_effect = new MonoEffect(handleWarnings, "warn");
const fatal_effect = new MonoEffect(handleFatal, "fatal");
const poly_effect = new PolyEffect();

poly_effect.add(warnings_effect);
poly_effect.add(fatal_effect);

const logger = root_logger.topic("target_module_name", {
  level: "info",
  effect: poly_effect,
});

logger.warn("Example warning");
logger.fatal("Nope, I'm dead");

// Output:
// 2024-07-26T18:47:01.978Z [WRN] target_module_name Example warning
// Warning has been recorded and saved
// 2024-07-26T18:47:01.978Z [FTL] target_module_name Nope, I'm dead
// Warning has been recorded and saved
// x_x

You can use PolyEffect to execute both parent and current effects. This will allow you to bypass the configuration inheritance limitation:

const poly_effect = new PolyEffect();
if (parent._config.effect) poly_effect.add(parent._config.effect);
poly_effect.add(() => { /* New effect */ });

const child = parent.topic("child", {
  ...parent._config,
  effect: poly_effect,
});

License

MIT