truncateWords

1/**
2 * Truncates a string to a maximum number of words and appends an ellipsis (or custom suffix).
3 *
4 * @param str - The input string.
5 * @param maxWords - The maximum number of words to keep.
6 * @param ellipsis - Optional string to append if truncated (defaults to '...').
7 * @returns Truncated string with suffix if it exceeded the word limit.
8 */
9export function truncateWords(str: string, maxWords: number, ellipsis: string = '...'): string {
10  if (maxWords < 0) {
11    throw new Error('maxWords must be non-negative');
12  }
13
14  const words = str.trim().split(/\s+/);
15  if (words.length <= maxWords) return str;
16
17  return words.slice(0, maxWords).join(' ') + ellipsis;
18}

1test('truncateWords - string with fewer words stays unchanged', () => {
2  expect(truncateWords('Hello world', 5)).toBe('Hello world');
3});
4
5test('truncateWords - string gets truncated to specified word count', () => {
6  expect(truncateWords('The quick brown fox jumps', 3)).toBe('The quick brown...');
7});
8
9test('truncateWords - custom ellipsis', () => {
10  expect(truncateWords('One two three four five', 2, ' (more)')).toBe('One two (more)');
11});
12
13test('truncateWords - exact number of words', () => {
14  expect(truncateWords('Alpha Beta Gamma', 3)).toBe('Alpha Beta Gamma');
15});
16
17test('truncateWords - trims leading/trailing whitespace', () => {
18  expect(truncateWords('  Hello   world!  ', 1)).toBe('Hello...');
19});
20
21test('truncateWords - zero word limit returns ellipsis only', () => {
22  expect(truncateWords('Some text here', 0)).toBe('...');
23});
24
25test('truncateWords - empty input string', () => {
26  expect(truncateWords('', 5)).toBe('');
27});
28
29test('truncateWords - negative word limit throws', () => {
30  expect(() => truncateWords('text', -2)).toThrow('maxWords must be non-negative');
31});