Level Control

/**
 * Set the current logging level
 * Disables all logging below the specified level
 * @param {LogLevelDesc} level - Level as string, number, or constant
 * @param {boolean} persist - Whether to persist level (default: true)
 * @throws {TypeError} When invalid level is provided
 */
setLevel(level: LogLevelDesc, persist?: boolean): void;

// Valid level descriptors
type LogLevelDesc = 
  | 0 | 1 | 2 | 3 | 4 | 5  // Numbers
  | 'trace' | 'debug' | 'info' | 'warn' | 'error' | 'silent'  // Lowercase strings
  | 'TRACE' | 'DEBUG' | 'INFO' | 'WARN' | 'ERROR' | 'SILENT';  // Uppercase strings

// Level constants
interface LogLevel {
  TRACE: 0;
  DEBUG: 1;
  INFO: 2;
  WARN: 3;
  ERROR: 4;
  SILENT: 5;
}

// Level number type
type LogLevelNumbers = 0 | 1 | 2 | 3 | 4 | 5;

import log from 'loglevel';

// String levels (case-insensitive)
log.setLevel("warn");
log.setLevel("ERROR");

// Numeric levels
log.setLevel(2); // INFO level

// Level constants
log.setLevel(log.levels.DEBUG);

// Disable persistence
log.setLevel("info", false);

// After setting to "warn", only warn and error messages show
log.debug("This won't appear");
log.warn("This will appear");
log.error("This will appear");

/**
 * Get current logging level as number
 * Useful for level-based conditional logic
 * @returns {LogLevelNumbers} Current level (0=TRACE, 1=DEBUG, 2=INFO, 3=WARN, 4=ERROR, 5=SILENT)
 */
getLevel(): LogLevelNumbers;

import log from 'loglevel';

log.setLevel("info");
const currentLevel = log.getLevel(); // Returns 2

// Conditional logging based on level
if (log.getLevel() <= log.levels.DEBUG) {
  const expensiveDebugData = generateDebugInfo();
  log.debug("Debug data:", expensiveDebugData);
}

// Level comparison
if (log.getLevel() < log.levels.ERROR) {
  log.warn("Non-critical warning message");
}

/**
 * Set default level without affecting persisted settings
 * Used for initial configuration that users can override
 * @param {LogLevelDesc} level - Level as string, number, or constant
 */
setDefaultLevel(level: LogLevelDesc): void;

import log from 'loglevel';

// Application initialization
log.setDefaultLevel("warn"); // Default for production

// If user previously set a level, it stays active
// If no persisted level exists, uses "warn"

// Useful for library initialization
function initializeLibrary() {
  log.setDefaultLevel("error"); // Libraries should be quiet by default
}

/**
 * Reset to default level and clear persisted level
 * Restores initial logging configuration
 */
resetLevel(): void;

import log from 'loglevel';

// User sets custom level
log.setLevel("trace");

// Later, reset to default
log.resetLevel(); // Returns to "warn" (or setDefaultLevel value)

// Clears localStorage/cookie persistence
// Useful for logout or session reset
function resetUserSession() {
  log.resetLevel();
}

/**
 * Enable all logging (equivalent to setLevel("trace"))
 * Shows maximum detail for debugging
 * @param {boolean} persist - Whether to persist setting (default: true)
 */
enableAll(persist?: boolean): void;

import log from 'loglevel';

// Development debugging
log.enableAll();

// Temporary debugging without persistence
log.enableAll(false);

// Console debugging session
// log.enableAll() - run this in browser console for full logging

/**
 * Disable all logging (equivalent to setLevel("silent"))
 * Completely suppresses log output
 * @param {boolean} persist - Whether to persist setting (default: true)
 */
disableAll(persist?: boolean): void;

import log from 'loglevel';

// Production silence
log.disableAll();

// Temporary quiet mode
log.disableAll(false);

// Performance-critical sections
function performanceCriticalOperation() {
  log.disableAll(false);
  // ... intensive operations ...
  log.setLevel("warn"); // Restore normal level
}

TRACE (0) ← Most verbose
  ↓
DEBUG (1)
  ↓
INFO (2)
  ↓
WARN (3) ← Default level
  ↓
ERROR (4)
  ↓
SILENT (5) ← No output

import log from 'loglevel';

// Set to INFO level
log.setLevel("info");

// These will output:
log.info("Info message");    // ✓ Level 2
log.warn("Warning");         // ✓ Level 3  
log.error("Error");          // ✓ Level 4

// These will be silent:
log.trace("Trace message");  // ✗ Level 0
log.debug("Debug info");     // ✗ Level 1

import log from 'loglevel';

// Persisted by default
log.setLevel("debug"); 
// Level survives page reload

// Temporary level (not persisted)
log.setLevel("trace", false);
// Resets to previous persistent level on reload

// Clear persistence
log.resetLevel();
// Removes stored level setting