Run results for: Array flatten implemenations

Run details:

User agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:85.0) Gecko/20100101 Firefox/85.0

Browser: Firefox 85

Operating system: Windows 7

Device Platform: Desktop

Date tested: 3 years ago

Test name	Executions per second
reduce + Array.prototype.concat	4453448.5 Ops/sec
Array.prototype.flat	7678996.5 Ops/sec
Manual copy by index #1	3520027.0 Ops/sec
Manual copy by index #2	10435720.0 Ops/sec
Manual copy with push	14530404.0 Ops/sec

Script Preparation code:

var params = [[ 1, 2 ], [ "hello", true, 7 ]];
function getTotal(arr) {
  let total = 0;
  for (let i = 0; i < arr.length; i++) {
    total += arr[i].length; 
  }
  return total;
}

Tests:

reduce + Array.prototype.concat
return params.reduce((acc, val) => acc.concat(val), []);
Array.prototype.flat
return params.flat();
Manual copy by index #1
const result = new Array(getTotal(params)); for (let i = 0; i < params.length; i++) { for (let j = 0; j < params[i].length; j++) { result[params[i].length * i + j] = params[i][j]; } } return result;
Manual copy by index #2
const result = new Array(getTotal(params)); for (let i = 0, k = 0; i < params.length; i++) { const arr = params[i]; for (let j = 0; j < arr.length; j++) { result[k] = arr[j]; k++; } } return result;
Manual copy with push
const result = []; for (let i = 0; i < params.length; i++) { const arr = params[i]; for (let j = 0; j < arr.length; j++) { result.push(arr[j]); } } return result;

Run results for: Array flatten implemenations

Compare the new ES6 spread operator with the traditional concat() method

reduce + Array.prototype.concat

Array.prototype.flat

Manual copy by index #1

Manual copy by index #2

Manual copy with push