Errors

The library uses MeraError for its documented failure modes. It carries a stable, machine-readable code alongside the usual message and optional cause. The codes are the contract; the message text is free to change between versions.

MeraError

class MeraError extends Error {
  readonly code: MeraErrorCode;
}

name is always "MeraError". When a lower-level failure triggered the error (a WebAuthn rejection, a Web Crypto failure), it is attached as cause.

isMeraError

import {
  getPasskeyPrfOutput,
  isMeraError,
} from "@category-labs/mera";

try {
  await getPasskeyPrfOutput({
    rpId: "account.example.com",
  });
} catch (error) {
  if (isMeraError(error) && error.code === "PRF_UNAVAILABLE") {
    // Point at a PRF-capable authenticator.
  }
  throw error;
}

isMeraError is a type guard: it narrows a caught value so code can be branched on.

Codes

PASSKEY_OPERATION_FAILED

WebAuthn failed, was cancelled, returned an unexpected credential, or the credential API is unavailable. Cancellation is the everyday case: the person dismissed the prompt.

CRYPTO_UNAVAILABLE

Web Crypto is unavailable. In practice this means the page is running outside a secure context (HTTPS, or localhost during development), or in a runtime without globalThis.crypto.

PRF_UNAVAILABLE

The authenticator did not enable PRF, or did not return a usable 32-byte PRF output. Authenticator support lists tested compatible stacks.

SESSION_ENDED

A signing call was made after the session’s end().

DECRYPT_FAILED

AES-GCM authentication failed while decrypting a vault: wrong key material or a tampered nonce/ciphertext pair.

INPUT_INVALID

A caller-supplied value at a public boundary did not satisfy a length, range, encoding, or curve constraint (a private key that is not a valid scalar, a public key that is not a valid point). Each function’s Errors section lists its specific conditions.

VAULT_FORMAT_INVALID

Untrusted vault data (JSON text or an object) was malformed, missing required fields, used a non-canonical encoding, or declared an unsupported version.