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uniq()

uniq<T>(array): T[]

Creates a duplicate-free version of an array.

note

Uses strict equality (===). First occurrence wins.

Type Parameters​

T: T​

The type of elements in the array.

Parameters​

array: readonly T[]​

The array to inspect.

Returns: T[]​

A new array with unique values, preserving order of first occurrence.

Since​

2.0.0

Performance​

O(n·k) linear scan for small arrays (≤200), O(n) with Set for larger ones.

Also known as​

dedupe (Effect) · uniq (Lodash, es-toolkit, Remeda, Ramda, Antfu) · unique (Radashi, Modern Dash)

Example​

uniq([1, 2, 2, 3, 4, 4, 5]);
// => [1, 2, 3, 4, 5]

uniq([11, 2, 3, 44, 11, 2, 3]);
// => [11, 2, 3, 44]

How it works?​

Removes duplicates using strict equality (===). First occurrence wins.

Use Cases​

Remove duplicate values from a collection 📌​

Remove repeated values from an array, keeping only the first occurrence. Essential for cleaning up lists of IDs, tags, or any primitive values.

const selectedIds = [3, 7, 3, 12, 7, 5, 12];

const uniqueIds = uniq(selectedIds);
// => [3, 7, 12, 5]

Clean up user tags 📌​

Ensure a tag list contains no repeated entries after user input. Perfect for form handling, content tagging, or search filters.

const userTags = ["react", "typescript", "react", "nodejs", "typescript"];

const cleanTags = uniq(userTags);
// => ["react", "typescript", "nodejs"]

Collect unique categories from a dataset​

Extract all distinct values after mapping a property from objects. Useful for building filter menus or faceted navigation.

const products = [
  { name: "Laptop", category: "electronics" },
  { name: "Shirt", category: "clothing" },
  { name: "Phone", category: "electronics" },
  { name: "Pants", category: "clothing" },
  { name: "Tablet", category: "electronics" },
];

const categories = uniq(products.map((p) => p.category));
// => ["electronics", "clothing"]

Deduplicate merged search results from multiple sources​

Remove duplicates when combining results from multiple search providers. Common when aggregating results from Algolia, Elasticsearch, and local DB.

const algoliaResults = ["doc-1", "doc-3", "doc-5", "doc-7"];
const dbResults = ["doc-2", "doc-3", "doc-4", "doc-5"];

const allResults = uniq([...algoliaResults, ...dbResults]);
// => ["doc-1", "doc-3", "doc-5", "doc-7", "doc-2", "doc-4"]

Ensure idempotent event processing​

Collect unique event IDs to avoid processing the same event twice. Critical for webhook handlers, message queues, and event-driven architectures.

const processedEventIds: string[] = [];

function handleEvent(eventId: string, payload: unknown) {
  const seen = uniq([...processedEventIds, eventId]);
  if (seen.length === processedEventIds.length) {
    return; // Already processed, skip
  }
  processedEventIds.push(eventId);
  processPayload(payload);
}