phone strategy

Purpose

The phone masking strategy anonymises phone numbers while preserving their formatting separators, making masked values easy to read in logs and audit trails. Only the last 4 digits are kept; all other digit positions are replaced with *. Non-digit characters (hyphens, spaces, parentheses, dots, +) pass through unchanged, so the output retains the same visual structure as the input regardless of locale or formatting convention.

Features

Last-4-digit preservation regardless of phone format.
Separator characters (-, , (, ), ., +) are preserved verbatim.
Handles international formats (+1-…), US formats ((555) 123-4567), and unformatted digit strings (5551234567).
No regex-based capture groups or lookaheads — single linear pass.

Usage: Basic Example

import { maskPhone } from '@suaveplan/data-masking/strategies/phone';

const masked = maskPhone('+1-555-123-4567', { fields: ['phone'], strategy: 'phone' });
// masked → '*-***-***-4567'

Usage: Advanced Example

import { maskPhone } from '@suaveplan/data-masking/strategies/phone';

// US format with parentheses
maskPhone('(555) 123-4567', { fields: ['phone'], strategy: 'phone' });
// → '(***) ***-4567'

// E.164 international
maskPhone('+447911123456', { fields: ['phone'], strategy: 'phone' });
// → '+*********3456'

// Unformatted
maskPhone('5551234567', { fields: ['phone'], strategy: 'phone' });
// → '******4567'

// No digits at all → passthrough
maskPhone('N/A', { fields: ['phone'], strategy: 'phone' });
// → 'N/A'

API Reference

`maskPhone(value, rule)`

function maskPhone(value: string, rule: MaskRule): string;

Parameter	Type	Description
`value`	`string`	The original phone number in any format.
`rule`	`MaskRule`	Driving rule (no fields are consumed by phone strategy).

Returns the masked phone string with last 4 digits preserved and all other digit positions replaced by *.

Does not throw. Returns the original value unchanged when no digit characters are found.

Implementation Notes

The strategy extracts all digits first to determine the keepFrom boundary (total digits minus 4), then makes a single linear pass over the original string to rebuild the result. This avoids multi-pass scanning and keeps the logic O(n).
Math.max(0, digits.length - 4) ensures that strings with 4 or fewer digits are returned with all digits preserved (no masking applied), matching the principle of least surprise.
The rule parameter is accepted to satisfy the uniform strategy interface but none of its fields are consumed.

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