pinojs/pino · error · Error

Levels comparison should be one of "ASC", "DESC" or "functio

Error message

Levels comparison should be one of "ASC", "DESC" or "function" type

What it means

pino's assertLevelComparison validates the levelComparison option used for sorting custom levels. It must be the string "ASC", "DESC", or a function; anything else (other strings, numbers, etc.) is rejected at logger creation time.

Source

Thrown at lib/levels.js:226

}

/**
 * Validates whether `levelComparison` is correct
 *
 * @throws Error
 * @param {SORTING_ORDER | Function} levelComparison - value to validate
 * @returns
 */
function assertLevelComparison (levelComparison) {
  if (typeof levelComparison === 'function') {
    return
  }

  if (typeof levelComparison === 'string' && Object.values(SORTING_ORDER).includes(levelComparison)) {
    return
  }

  throw new Error('Levels comparison should be one of "ASC", "DESC" or "function" type')
}

module.exports = {
  initialLsCache,
  genLsCache,
  levelMethods,
  getLevel,
  setLevel,
  isLevelEnabled,
  mappings,
  assertNoLevelCollisions,
  assertDefaultLevelFound,
  genLevelComparison,
  assertLevelComparison
}

View on GitHub (pinned to 5aa62305c5)

Solutions

Use the exact strings "ASC" or "DESC" (uppercase)
Pass a comparator function: levelComparison: (a, b) => a - b
Normalize config values: levelComparison: (raw || '').toUpperCase()

Example fix

// before
pino({ customLevels: { foo: 30 }, levelComparison: 'asc' });
// after
pino({ customLevels: { foo: 30 }, levelComparison: 'ASC' });

Defensive patterns

Strategy: validation

Validate before calling

const VALID = ['ASC', 'DESC'];
function assertLevelComparison(lc) {
  if (!(VALID.includes(lc) || typeof lc === 'function')) {
    throw new TypeError('levelComparison must be "ASC", "DESC", or a function');
  }
}

Type guard

function isValidLevelComparison(v) { return v === 'ASC' || v === 'DESC' || typeof v === 'function'; }

Try / catch

try { const logger = pino(opts); } catch (e) { if (/Levels comparison/.test(e.message)) { opts.levelComparison = 'ASC'; } throw e; }

Prevention

Normalize case when levelComparison comes from config: String(raw).toUpperCase()
Use TypeScript union type: 'ASC' | 'DESC' | ((a: number, b: number) => number)
Only pass levelComparison when configuring custom levels

When it happens

Trigger: Passing pino({ levelComparison: 'asc' }) (lowercase), levelComparison: true, levelComparison: 1, or any value not in SORTING_ORDER and not a function.

Common situations: Typos or wrong casing when configuring custom levels sort order; passing a comparison value read from config that is not normalized; misunderstanding that only exact "ASC"/"DESC" strings are accepted.

Understand the failure class

Background: Invalid enum value errors: "Unknown type", "Invalid scope", "must be one of" — when a string is not on the library's allowed list — this error's family across 23 libraries.

Related errors

AI-assisted analysis of pinojs/pino@5aa62305c5 (2026-09-02). Data as JSON: /api/errors/b4468643c2b0ff8b. Report an issue: GitHub.