maskString

1/**
2 * Masks a string by replacing all but the last 'visibleCount' characters
3 * with a mask character.
4 * If the string is shorter than or equal to 'visibleCount',
5 * the original string is returned.
6 *
7 * @param str - The input string to mask.
8 * @param visibleCount - Number of characters to leave unmasked at the end (default is 4).
9 * @param maskChar - The character to use for masking (default is '*').
10 * @returns The masked string.
11 */
12export function maskString(
13  str: string,
14  visibleCount: number = 4,
15  maskChar: string = '*'
16): string {
17  const maskedLength = Math.max(str.length - visibleCount, 0);
18  return maskChar.repeat(maskedLength) + str.slice(-visibleCount);
19}

1test('maskString - masks all but last 4 characters by default', () => {
2  expect(maskString('1234567890')).toBe('******7890');
3});
4
5test('maskString - custom visibleCount', () => {
6  expect(maskString('abcdef', 2)).toBe('****ef');
7});
8
9test('maskString - custom mask character', () => {
10  expect(maskString('secret', 3, '#')).toBe('###ret');
11});
12
13test('maskString - visibleCount greater than string length', () => {
14  expect(maskString('abc', 5)).toBe('abc');
15});
16
17test('maskString - empty string', () => {
18  expect(maskString('', 4)).toBe('');
19});
20
21test('maskString - visibleCount = 0 masks everything', () => {
22  expect(maskString('12345', 0)).toBe('*****');
23});