Run results for: Spreading + Concat vs flat

Run details:

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:80.0) Gecko/20100101 Firefox/80.0

Browser: Firefox 80

Operating system: Mac OS X 10.13

Device Platform: Desktop

Date tested: 4 years ago

Test name	Executions per second
Spreading + concat	735.1 Ops/sec
Flat	689.0 Ops/sec

Script Preparation code:

let array2D = [];
const n = 1000;
const c = 100;
for (let i = 0; i < n; i++) {
  let array1D = [];
  for (let k = 0; k < c; k++) {
    array1D.push(k); 
  }
  array2D.push(array1D);
}
window.array2D = array2D;

Tests:

Spreading + concat
let result1 = [].concat(...window.array2D);
Flat
let result = window.array2D.flat();

Run results for: Spreading + Concat vs flat

Spreading + concat

Flat