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:

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

[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.

A simple polyfill from the proposal repo write in TypeScript.

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