Run results for: Concat vs push(...) vs flat for large arrays of arrays

Run details:

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:101.0) Gecko/20100101 Firefox/101.0

Browser: Firefox 101

Operating system: Windows

Device Platform: Desktop

Date tested: 2 years ago

Test name	Executions per second
Control (for push)	437815.9 Ops/sec
Concat	251685.0 Ops/sec
Spread	149866.5 Ops/sec
Flat	619813.5 Ops/sec

Script Preparation code:

window.top.tests = {control:[], concat:[], spread:[], flat: []};
window.test = (new Array(10)).fill(null);
window.arrays = (new Array(10)).fill(window.test);
window.cutoff = 5000;

Tests:

Control (for push)
window.top.tests.control = window.arrays.reduce((acc, arr) => { acc.push(...arr); return acc; }, []); if (window.top.tests.control.length > window.cutoff) { window.top.tests.control = []; console.log('reset control'); }
Concat
window.top.tests.concat = window.arrays.reduce((acc, arr) => acc.concat(arr), []); if (window.top.tests.concat.length > window.cutoff) { window.top.tests.concat = []; console.log('reset concat'); }
Spread
window.top.tests.spread = window.arrays.reduce((acc, arr) => [...acc, ...arr], []); if (window.top.tests.spread.length > window.cutoff) { window.top.tests.spread = []; console.log('reset spread'); }
Flat
window.top.tests.flat = window.arrays.flat(); if (window.top.tests.flat.length > window.cutoff) { window.top.tests.flat = []; console.log('reset flat'); }

Run results for: Concat vs push(...) vs flat for large arrays of arrays

Comparing the various ways to append to a large array

Control (for push)

Concat

Spread

Flat