Run results for: String concatenation keys vs Multidimensional array keys2

Run details:

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/88.0.4324.96 Safari/537.36 Edg/88.0.705.50

Browser: Chrome 88

Operating system: Mac OS X 10.15.7

Device Platform: Desktop

Date tested: 3 years ago

Test name	Executions per second
String concatenation keys	5.5 Ops/sec
Multidimensional array keys	12.8 Ops/sec

Script Preparation code:

var numberList = Array(1000).fill().map((x, i) => i);

var concatList = numberList.reduce((acc, i1) => {
  numberList.forEach(i2 => { acc[`${i2}_${i2}`] = 'string'; });
  return acc;
}, {});

var twoDList = numberList.reduce((acc, i1) => {
  numberList.forEach((i2) => {
    if (!acc[i1]) acc[i1] = {};
    acc[i1][i2] = 'string';
  });
  return acc;
}, {});

Tests:

String concatenation keys
numberList.forEach((i1) => { numberList.forEach((i2) => { const variable = concatList[`${i2}_${i2}`]; }); });
Multidimensional array keys
numberList.forEach((i1) => { numberList.forEach((i2) => { const variable = twoDList[i2][i2]; }); });