Array deduplication proposal

ECMAScript proposal for Deduplicating method of Array.

!Proposal Stage-1
![CI & CD][1]

![NPM][2]

Motivation

Deduplication is one of the most common requirements in Data processing, especially in large Web Apps nowadays.

In Lodash, uniq methods are also [very popular][3]:

| # | Name | Downloads |
| --- | -------- | --------- |
| 1 | uniq | 5,546,070 |
| 7 | uniqby | 447,858 |
| 28 | uniqwith | 15,077 |

But [...new Set(array)] in ECMAScript 6 isn't enough for Non-primitive values, and now, we may need a Array.prototype.uniqueBy().

Core features

While Array.prototype.uniqueBy() invoked with:

1. no parameter, it'll work as [...new Set(array)];

2. one index-key parameter (Number, String or Symbol), it'll get values from each array element with the key, and then deduplicates the origin array based on these _values_;

3. one function parameter, it'll call this function for each array element, and then deduplicates the origin array based on these _returned values_.

Notice:

- the Returned value is a new array, no mutation happens in the original array
- Empty/nullish items are treated as nullish values
- 0 & -0 are treated as the same
- All NaNs are treated as the same

Typical cases

``JavaScript
[1, 2, 3, 3, 2, 1].uniqueBy(); // [1, 2, 3]

const data = [
{ id: 1, uid: 10000 },
{ id: 2, uid: 10000 },
{ id: 3, uid: 10001 }
];

data.uniqueBy('uid');
// [
// { id: 1, uid: 10000 },
// { id: 3, uid: 10001 }
// ]

data.uniqueBy(({ id, uid }) => ${id}-${uid});
// [
// { id: 1, uid: 10000 },
// { id: 2, uid: 10000 },
// { id: 3, uid: 10001 }
// ]
``

Polyfill

A polyfill is available in the [core-js][4] library. You can find it in the [ECMAScript proposals section][5].

A simple polyfill from the proposal repo write in TypeScript.

Proposer

- Author: @TechQuery
- Champion: @Jack-Works

[1]: https://github.com/tc39/proposal-array-unique/actions/workflows/main.yml
[2]: https://nodei.co/npm/array-unique-proposal/
[3]: https://github.com/AndrewRot/lodash-function-usage/blob/9ec92a7980e321f8a32dd62e13addd6562ba4612/README.md
[4]: https://github.com/zloirock/core-js
[5]: https://github.com/zloirock/core-js#array-deduplication