Run results for: Concat v Push

Run details:

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Safari/537.36

Browser: Chrome 69

Operating system: Windows

Device Platform: Desktop

Date tested: 5 years ago

Test name	Executions per second
Concat	411.2 Ops/sec
Push	31836.2 Ops/sec

Script Preparation code:

emptyArray = [];
flatMapConcat = f => xs => xs.reduce((r, x) => r.concat(f(x)), emptyArray);

flatMapPush = f => xs => xs.reduce((r, x) => {
  f(x).forEach(y => {r.push(y)})
  return r;
}, []);

inc = x => [x, x + 1];

arr = Array(1000).fill(1);

Tests:

Concat
r1 = flatMapConcat(inc)(arr)
Push
r2 = flatMapPush(inc)(arr)