Run results for: Array flatten implementations [high volume]

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 + concat	12.2 Ops/sec
flat	406.8 Ops/sec
Manual copy by index #1	377.1 Ops/sec
Manual copy by index #2	527.3 Ops/sec
Manual copy with push	466.1 Ops/sec
reduce + spread	4.3 Ops/sec

Script Preparation code:

var params = [];
for (let i = 0; i < 100; i++) {
    const arr = [];
    for (let j = 0; j < 1000; j++) {
        arr.push(999 * Math.random());
    }
    params.push(arr);
}

function getTotal(arr) {
    let total = 0;
    for (let i = 0; i < arr.length; i++) {
        total += arr[i].length;
    }
    return total;
}

Tests:

reduce + concat
return params.reduce((acc, val) => acc.concat(val), []);
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;
reduce + spread
return params.reduce((acc, val) => [...acc, ...val], []);

Run results for: Array flatten implementations [high volume]

Compare various ways to flatten nested arrays 1 level deep.

reduce + concat

flat

Manual copy by index #1

Manual copy by index #2

Manual copy with push

reduce + spread