GitHub - tc39/proposal-array-unique: ECMAScript proposal for Deduplicating method of Array (original) (raw)

Array deduplication proposal

ECMAScript proposal for Deduplicating method of Array.

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:

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

While Array.prototype.uniqueBy() invoked with:

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

[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 } // ]

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