validateBsn

Validates a Dutch BSN (Burgerservicenummer) against the elfproef — in the browser, without a round trip.

import { validateBsn } from '@conduction/nextcloud-vue'

const result = validateBsn('111222333')
// { isFormallyValid: true, elevenTestScore: 0, errorCode: null, maskedBsn: '***2223*' }

Param	Type	Description
input	string	The candidate BSN. null/undefined are tolerated and reported invalid.

Returns { isFormallyValid, elevenTestScore, errorCode, maskedBsn }.

Field	Type	Description
isFormallyValid	boolean	Nine digits satisfying the elfproef.
elevenTestScore	number	The modulo — 0 when valid, -1 when the input was not nine digits.
errorCode	string|null	BSN_ERROR_LENGTH, BSN_ERROR_CHECKSUM, or null.
maskedBsn	string	See maskBsn. The raw input is never echoed back.

This does not replace server-side validation

It is a UX affordance. OpenRegister's bsn schema property validator remains the write boundary, and anything reaching the API directly never touches a browser. What this replaces is a validation endpoint whose only job is to return a yes/no about a checksum — a network hop per keystroke that also puts special-category personal data on the wire.

A formally valid BSN is not an issued one. The elfproef proves the number is well-formed; only a BRP lookup establishes that it belongs to a person.

The ninth digit weighs −1

sum(digit[i] × (9 − i)) for i = 0..7, then subtract digit[8]; valid when divisible by eleven. An implementation that adds the last digit accepts roughly one in eleven invalid numbers, which is why the test suite pins cases that separate the two weightings.