formatToHiddenDigits
The formatToHiddenDigits function is a utility for masking or hiding specific digits within a string while preserving non-digit characters and the overall structure. This function is particularly useful for displaying sensitive information like credit card numbers, phone numbers, or social security numbers in a secure manner.
Import
import { formatToHiddenDigits } from "@arkyn/shared";
Parameters
The function accepts the following parameters:
value (required)
The input string containing digits to be masked. This can include any combination of digits and non-digit characters. Only the digits will be affected by the masking, while all other characters (such as hyphens, spaces, or parentheses) remain unchanged.
Type: string
options (optional)
An optional configuration object to customize the masking behavior.
Type: object
options.range (optional)
Specifies which digits should be hidden. This parameter accepts two formats:
- A single positive number hides the first n digits (e.g.,
3 hides the first three digits)
- A single negative number hides the last n digits (e.g.,
-4 hides the last four digits)
- A tuple
[start, end] specifies the exact range of digit positions to hide (inclusive, 1-indexed)
Type: number | [number, number]
Default: 3
options.hider (optional)
The character used to replace the hidden digits. This can be any single character that you want to use as a mask.
Type: string
Default: "*"
Usage example
The function returns a formatted string with the specified digits replaced by the hider character, while preserving all non-digit characters in their original positions.
Type: string
import { formatToHiddenDigits } from "@arkyn/shared";
const result = formatToHiddenDigits("123-456-7890");
console.log(result);
Notes
The function only counts and masks actual digit characters (0-9), completely ignoring all other characters like spaces, hyphens, parentheses, or letters in the range calculation.
Digit positions are counted from 1, not 0, making the range specification more intuitive (e.g., [1, 3] hides the first three digits).
When using a positive single number for the range, digits are hidden from the beginning; when using a negative number, digits are hidden from the end.
The structure and formatting of the original string are completely preserved - only the digit characters within the specified range are replaced.
