Run results for: flatmap vs concat and spread operator

Run details:

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/115.0.0.0 Safari/537.36

Browser: Chrome 115

Operating system: Mac OS X 10.15.7

Device Platform: Desktop

Date tested: 2 years ago

concat with spread

6.8M/s

flatmap

2.0M/s

View exact numbers

Test name	Executions per second
✓ concat with spread	6,828,565 Ops/sec
flatmap	2,016,433 Ops/sec

Script Preparation code:

var arrayArray = [{
        entries: [{
            id: 1
        }, {
            id: 2
        }]
    },
    {
        entries: [{
            id: 3
        }, {
            id: 4
        }]
    },
    {
        entries: [{
            id: 5
        }, {
            id: 6
        }]
    }
];

Tests:

flatmap
arrayArray.flatMap((item) => item.entries.map((entry) => entry.id));
concat with spread
[].concat(...arrayArray.map((item) => item.entries.map((entry) => entry.id)));