tessl/npm-log

Universal pluggable logging utility with configurable levels and namespacing support

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Overview

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Files

Core Logging

Name: tessl/npm-log
Author: tessl

Primary logging functionality with five severity levels based on syslog standards. Supports printf-style message formatting and provides both callable logger functions and level-specific methods.

Capabilities

Main Logger Function

The default export is a callable logger function operating at 'info' level.

/**
 * Main logger function - logs at 'info' level
 * @param {*} message - Primary message (string with printf placeholders or any value)
 * @param {...*} args - Arguments for printf-style formatting
 */
function log(message, ...args);

Usage Examples:

const log = require("log");

// Simple string logging
log("Application started");
log("User logged in");

// Printf-style formatting
log("User %s logged in with ID %d", "alice", 123);
log("Processing %d items", 42);
log("Config: %j", { debug: true, port: 3000 });

Level-Specific Loggers

Each logger provides access to all five logging levels as properties/methods.

/**
 * Debug level logger - for debugging information (hidden by default)
 * @param {*} message - Message to log
 * @param {...*} args - Arguments for formatting
 */
log.debug(message, ...args);

/**
 * Info level logger - for informational messages (hidden by default)  
 * @param {*} message - Message to log
 * @param {...*} args - Arguments for formatting
 */
log.info(message, ...args);

/**
 * Notice level logger - for significant conditions (visible by default)
 * @param {*} message - Message to log
 * @param {...*} args - Arguments for formatting
 */
log.notice(message, ...args);

/**
 * Warning level logger - for warning conditions (visible by default)
 * @param {*} message - Message to log  
 * @param {...*} args - Arguments for formatting
 */
log.warning(message, ...args);

/**
 * Warn level logger - alias for warning level
 * @param {*} message - Message to log
 * @param {...*} args - Arguments for formatting
 */
log.warn(message, ...args);

/**
 * Error level logger - for error conditions (visible by default)
 * @param {*} message - Message to log
 * @param {...*} args - Arguments for formatting
 */
log.error(message, ...args);

Usage Examples:

const log = require("log");

// Different severity levels
log.error("Database connection failed: %s", error.message);
log.warning("Deprecated API used in %s", functionName);
log.notice("Server started on port %d", 3000);
log.info("Processing request %s", requestId);
log.debug("Variable state: %j", debugObject);

// Level chaining - all return the same logger instance
log.info === log;           // true
log.error.info === log;     // true
log.warning.debug.error === log.error;  // true

Level Properties

Each logger exposes properties describing its level configuration.

/**
 * Current logger level name
 * @type {string}
 */
log.level;

/**
 * Numeric index of logger level (0=error, 1=warning, 2=notice, 3=info, 4=debug)
 * @type {number}
 */
log.levelIndex;

/**
 * Reference to the root logger for this level
 * @type {Logger}
 */
log.levelRoot;

Usage Examples:

const log = require("log");

console.log(log.level);        // "info"
console.log(log.levelIndex);   // 3

console.log(log.error.level);      // "error" 
console.log(log.error.levelIndex); // 0

// Root logger reference
const nsLogger = log.get("mylib");
console.log(nsLogger.levelRoot === log);  // true

Level Management

Methods for inspecting and managing logger level initialization.

/**
 * Check if a logger for the specified level has been initialized
 * @param {string} level - Level name to check
 * @returns {boolean} True if level logger exists
 */
log.isLevelInitialized(level);

/**
 * Get all initialized level loggers for the current namespace
 * @returns {Logger[]} Array of initialized logger instances
 */
log.getAllInitializedLevels();

Usage Examples:

const log = require("log");

// Check level initialization
console.log(log.isLevelInitialized("info"));    // true
console.log(log.isLevelInitialized("debug"));   // false (until first access)
console.log(log.isLevelInitialized("custom"));  // false (not a valid level)

// Access debug logger to initialize it
log.debug("test");

// Now debug is initialized  
console.log(log.isLevelInitialized("debug"));   // true

// Get all initialized levels
const levels = log.getAllInitializedLevels();
console.log(levels.map(l => l.level)); // ["info", "debug"]

Message Formatting

The log package supports printf-style message formatting with the following placeholders:

%s - String
%d - Number (integer or floating point value)
%i - Integer
%f - Floating point value
%j - JSON (with circular reference handling)
%o - Object representation with hidden properties
%O - Object representation without hidden properties
%% - Literal percent sign

Formatting Examples:

const log = require("log");

// String formatting
log("Hello %s", "world");                    // "Hello world"

// Number formatting  
log("Count: %d, Price: %f", 42, 19.99);      // "Count: 42, Price: 19.99"

// JSON formatting
log("Config: %j", { port: 3000, debug: true }); // "Config: {"port":3000,"debug":true}"

// Object formatting
log("User: %o", user);                       // Detailed object output
log("Simple: %O", user);                     // Simple object output

// Literal percent
log("Progress: 50%%");                       // "Progress: 50%"