how to speed up uniqBy method in javascript?

Question

I've implement uniqBy method as following.

Array.prototype.uniqBy = function (iteratee) {
  let uniques = [];
  for (let a of this) {
    const mappedUniques = uniques.map(iteratee);
    if (!mappedUniques.includes(iteratee(a))) {
      uniques.push(a);
    }
  }
  return uniques;
}

How to use this method:

let arrays = [
    {id: 1, value: 'm'},
    {id: 2, value: 'cm'},
    {id: 3, value: 'km'},
    {id: 2, value: 'cm2'}
];

console.log(arrays.uniqBy(x => {return x.id}));

After this, will removed duplicate ids. So

[
    {id: 1, value: 'm'},
    {id: 2, value: 'cm'},
    {id: 3, value: 'km'}
]

But it's performance is not good.
Where is more good performance method or library?

Anyone please advice. Thanks.

Please don't extend array prototype unless you are pulling in a legacy shim — Jeremy J Starcher, Feb 01 '21 at 14:41
@JeremyJStarcher I've updated my post. And I don't want change result. just improve speed. — Daniel.Wang, Feb 01 '21 at 14:47

score 2 · Accepted Answer · answered Feb 01 '21 at 14:50

Make a separate Set of the unique primitives instead of using an array; set lookup is much, much faster than an array's .includes. Instead of mapping the uniques each time in the loop, use the separate Set.

function (iteratee) {
    const uniquePrimitives = new Set();
    return this.filter((item) => {
        const prim = iteratee(item);
        if (!uniquePrimitives.has(prim)) {
            uniquePrimitives.add(prim);
            return true;
        }
    });
}

As has been said, I'd highly recommend against mutating built-in prototypes.

how to speed up uniqBy method in javascript?

1 Answers1