Run results for: Object.groupBy vs manual groupBy object vs manual groupBy Map

Test name	Executions per second
✓ Manual groupBy map 1	82,303 Ops/sec
Manual groupBy obj	75,669 Ops/sec
Manual groupBy map 2	71,309 Ops/sec
Object.groupBy	48,293 Ops/sec

Script Preparation code:

function groupByObj(array, mapper) {
    return array.reduce(
        (acc, item) => {
            const key = mapper(item);
            const items = acc[key] ?? (acc[key] = []);
            items.push(item);
            return acc;
        }, {},
    );
}

function groupByMap1(array, mapper) {
    return array.reduce(
        (acc, item) => {
            const key = mapper(item);
            let items = acc.get(key);
            if (!items) {
              items = []
              acc.set(key, items)
            }
            items.push(item);
            return acc;
        }, new Map(),
    );
}

function groupByMap2(array, mapper) {
    return array.reduce(
        (acc, item) => {
            const key = mapper(item);
            if (!acc.has(key)) {
              acc.set(key, [item])
            } else { acc.get(key).push(item) }
            return acc;
        }, new Map(),
    );
}

function makeid(length) {
    var result = '';
    var characters = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
    var charactersLength = characters.length;
    for (var i = 0; i < length; i++) {
        result += characters.charAt(Math.floor(Math.random() * charactersLength));
    }
    return result;
}

function randomIntFromInterval(min, max) { // min and max included 
    return Math.floor(Math.random() * (max - min + 1) + min);
}

var data = []

for (let i = 0; i < 1000; i++) {
    data.push({
        name: makeid(randomIntFromInterval(5, 16)),
        age: randomIntFromInterval(1, 100),
        occupation: Math.random() > 0.8 ? makeid(randomIntFromInterval(5, 16)) : null
    })
}

Tests:

Object.groupBy
return Object.groupBy(data, item => item.occupation)
Manual groupBy obj
return groupByObj(data, item => item.occupation)
Manual groupBy map 1
return groupByMap1(data, item => item.occupation)
Manual groupBy map 2
return groupByMap2(data, item => item.occupation)

Run results for: Object.groupBy vs manual groupBy object vs manual groupBy Map

Object.groupBy

Manual groupBy obj

Manual groupBy map 1

Manual groupBy map 2