Concat vs push(...) vs flat for large arrays of arrays

Comparing the various ways to append to a large array
one year ago
User agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:109.0) Gecko/20100101 Firefox/110.0
Test name Executions per second
Control (for push) 242991.2 Ops/sec
Concat 158066.1 Ops/sec
Spread 85451.8 Ops/sec
Flat 339913.8 Ops/sec
Script Preparation code:
AخA
 
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'); }
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