Benchmark: flatMap vs reduce (concat) vs reduce (spread) vs reduce (push)

Script Preparation code:

var arr = Array(10000).fill(1)

Tests:

Reduce concat
arr.reduce((acc, x, index) => acc.concat(x, index % 2 ? x : []), [])
FlatMap
arr.flatMap((x, index) => [x, index % 2 && x]).filter(Boolean)
Reduce push
arr.reduce((acc, x, index) => { acc.push(x); if(index % 2) { acc.push(x) } return acc; }, [])
Reduce spread
arr.reduce((acc, x, index) => index % 2 ? [x,...acc] : acc, [])

Rendered benchmark preparation results:

Previous results

Latest run results:

Run details: (Test run date: 2 years ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/122.0.0.0 Safari/537.36

Browser/OS: Chrome 122 on Mac OS X 10.15.7

Reduce push

27K/s

FlatMap

2K/s

Reduce spread

28/s

Reduce concat

7/s

View exact numbers

flatMap vs reduce (concat) vs reduce (spread) vs reduce (push) (version: 0)