unique

1/**
2 * Removes duplicate primitive values from an array.
3 *
4 * @param arr - The input array of primitive values.
5 * @returns A new array containing only unique values.
6 */
7export function unique<T>(arr: T[]): T[] {
8  return Array.from(new Set(arr));
9}

• Efficient duplicate removal using Set

  Utilizes JavaScript's Set, which inherently enforces uniqueness, making the implementation both concise and performant.

• Linear time complexity O(n)

  The use of Set avoids nested iterations, offering significantly better performance than methods like .includes() or .indexOf().

• Minimalistic and highly readable

  The function is extremely concise, making it easy to understand and maintain.

• Supports all primitive types

  Works correctly with numbers, strings, booleans, null, undefined, and symbol, including mixed-type arrays such as [1, '1', true].

• Immutable by design

  Returns a new array, preserving the original input. This is important for functional programming patterns and React state management.

Tests | Examples

1test('unique - removes duplicate strings', () => {
2  expect(unique(['a', 'b', 'a', 'c'])).toEqual(['a', 'b', 'c']);
3});
4
5test('unique - returns same array when no duplicates', () => {
6  expect(unique([1, 2, 3])).toEqual([1, 2, 3]);
7});
8
9test('unique - works with empty array', () => {
10  expect(unique([])).toEqual([]);
11});
12
13test('unique - removes duplicate booleans', () => {
14  expect(unique([true, false, true])).toEqual([true, false]);
15});
16
17test('unique - removes duplicate mixed values', () => {
18  expect(unique([1, '1', 1])).toEqual([1, '1']);
19});

Common Use Cases

• Deduplicating identifiers

  Useful when aggregating data from different sources and ensuring IDs or keys are unique.

• Cleaning user input

  When users provide lists of items (tags, emails, filters), this utility can prevent duplicates from being stored or processed.

• Normalizing API responses

  Helps ensure data integrity by removing repeated values after merging responses from multiple endpoints.

• Generating unique filter options

  Commonly used to extract unique categories, tags, or types from data sets for UI filters or dropdowns.