countOccurrences

1/**
2 * Counts how many times a substring appears in a string.
3 *
4 * @param str - The string to search within.
5 * @param subStr - The substring to count.
6 * @returns Number of non-overlapping occurrences of the substring.
7 *
8 * @throws Error if subStr is an empty string.
9 */
10export function countOccurrences(str: string, subStr: string): number {
11  if (subStr === '') {
12    throw new Error('Substring cannot be an empty string');
13  }
14
15  return str.split(subStr).length - 1;
16}

1test('countOccurrences - basic usage', () => {
2  expect(countOccurrences('banana', 'na')).toBe(2);
3});
4
5test('countOccurrences - no matches', () => {
6  expect(countOccurrences('hello world', 'xyz')).toBe(0);
7});
8
9test('countOccurrences - full match', () => {
10  expect(countOccurrences('aaa', 'a')).toBe(3);
11});
12
13test('countOccurrences - special characters', () => {
14  expect(countOccurrences('a*b*c*', '*')).toBe(3);
15});
16
17test('countOccurrences - empty substring throws', () => {
18  expect(() => countOccurrences('abc', '')).toThrow('Substring cannot be an empty string');
19});