fromQueryParams

1/**
2 * Parses a query string into an object.
3 * Supports repeated keys as arrays.
4 *
5 * @param query - The query string (with or without leading '?').
6 * @returns An object with parsed query parameters.
7 */
8export function fromQueryParams(query: string): Record<string, string | string[]> {
9  const result: Record<string, string | string[]> = {};
10
11  query
12    .replace(/^\?/, '') // remove leading '?'
13    .split('&')
14    .filter(Boolean)
15    .forEach(part => {
16      const [rawKey, rawVal] = part.split('=');
17      const key = decodeURIComponent(rawKey);
18      const value = decodeURIComponent(rawVal || '');
19
20      if (result[key] === undefined) {
21        result[key] = value;
22      } else if (Array.isArray(result[key])) {
23        (result[key] as string[]).push(value);
24      } else {
25        result[key] = [result[key] as string, value];
26      }
27    });
28
29  return result;
30}

1test('fromQueryParams - single pair', () => {
2  expect(fromQueryParams('q=test')).toEqual({ q: 'test' });
3});
4
5test('fromQueryParams - multiple pairs', () => {
6  expect(fromQueryParams('q=js&sort=asc')).toEqual({ q: 'js', sort: 'asc' });
7});
8
9test('fromQueryParams - handles repeated keys as arrays', () => {
10  expect(fromQueryParams('tag=a&tag=b')).toEqual({ tag: ['a', 'b'] });
11});
12
13test('fromQueryParams - decodes values', () => {
14  expect(fromQueryParams('q=C%23%20%26%20Java')).toEqual({ q: 'C# & Java' });
15});
16
17test('fromQueryParams - handles empty value', () => {
18  expect(fromQueryParams('flag=')).toEqual({ flag: '' });
19});
20
21test('fromQueryParams - handles leading ?', () => {
22  expect(fromQueryParams('?a=1&b=2')).toEqual({ a: '1', b: '2' });
23});
24
25test('fromQueryParams - empty string returns empty object', () => {
26  expect(fromQueryParams('')).toEqual({});
27});