Events & Error handling

Events

The SDK emits events so you can show spinners and handle analytics:

client.on('start', (payload) => {
  console.log('Started:', payload.operation)  // 'signUp' | 'signIn' | 'enroll'
  showSpinner()
})

client.on('success', (payload) => {
  console.log('Success:', payload.operation)
  hideSpinner()
})

client.on('error', (payload) => {
  console.error('Error:', payload.error)
  hideSpinner()
  showError(payload.error.message)
})

// Unsubscribe
const unsubscribe = client.on('start', handler)
unsubscribe()

Events: 'start', 'success', 'error', 'cancelled'.

Error handling

All methods return Result<T, TryMellonError>. Check result.ok and use result.error.code:

import { isTryMellonError } from '@trymellon/js'

const result = await client.signIn({ externalUserId: 'user_123' })

if (!result.ok) {
  const error = result.error
  switch (error.code) {
    case 'USER_CANCELLED':
      console.log('User cancelled')
      break
    case 'NOT_SUPPORTED':
      await client.otp.send({
        userId: 'user_123',
        email: '[email protected]',
      })
      break
    case 'PASSKEY_NOT_FOUND':
      await client.signUp({ externalUserId: 'user_123' })
      break
    case 'NETWORK_FAILURE':
      // Often caused by unallowed Origin in TryMellon dashboard (CORS rejection)
      console.error('Network error:', error.details)
      break
    case 'TIMEOUT':
      console.error('Operation timed out')
      break
    default:
      console.error(error.code, error.message)
  }
  return
}

// result.value has sessionToken, user, etc.

Error codes

Code	Description
`NOT_SUPPORTED`	WebAuthn not available in this environment
`USER_CANCELLED`	User cancelled the operation
`PASSKEY_NOT_FOUND`	No passkey found for this user
`SESSION_EXPIRED`	Session or QR session expired
`NETWORK_FAILURE`	Network error (SDK retries with backoff)
`INVALID_ARGUMENT`	Invalid argument in config, options, or origin not allowed
`TIMEOUT`	Operation timed out
`ABORT_ERROR`	Operation aborted via AbortSignal or browser `AbortError`
`CHALLENGE_MISMATCH`	Link already used, replayed, or context hash mismatch
`RATE_LIMIT_EXCEEDED`	Too many requests — SDK backs off and retries automatically
`TICKET_NOT_FOUND`	Enrollment ticket not found or invalid
`TICKET_EXPIRED`	Enrollment ticket has expired
`TICKET_ALREADY_USED`	Enrollment ticket was already consumed
`PIN_MISMATCH`	Bridge presence PIN does not match
`PIN_LOCKED`	Bridge PIN locked after too many failed attempts
`BRIDGE_SESSION_EXPIRED`	Bridge session expired or not found
`ACTION_CHALLENGE_EXPIRED`	Action signing challenge TTL exceeded (default 5 min) — issue a new challenge
`ACTION_ALREADY_CLAIMED`	Action challenge already verified — anti-replay; each challenge is single-use
`ACTION_PAYLOAD_MISMATCH`	Payload hash signed by the device doesn’t match what the server issued
`FORBIDDEN`	Access denied — missing required role or scope
`SERVER_ERROR`	Unrecoverable server-side error
`UNKNOWN_ERROR`	Unexpected error — check `error.details` for context

Troubleshooting CORS & Network Errors

If your users experience silent failures or you see NETWORK_FAILURE in the SDK with a (null) status in your browser’s Network tab for OPTIONS preflight requests, this typically means CORS rejection.

Ensure that the domain from which the SDK is running (e.g., https://your-app.com) has been added to your Application’s Allowed Origins list in the TryMellon dashboard. TryMellon enforces strict dynamic origin validation to protect your users.

Cancel with AbortSignal

const controller = new AbortController()
setTimeout(() => controller.abort(), 10000)

const result = await client.signUp({
  externalUserId: 'user_123',
  signal: controller.signal,
})
if (!result.ok && result.error.code === 'ABORT_ERROR') {
  console.log('Cancelled')
}