Run results for: for, for of, forEach, and reduce. Each with and without reduced variable re-declarations.

Run details:

User agent: Mozilla/5.0 (iPhone; CPU iPhone OS 13_7 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) CriOS/85.0.4183.92 Mobile/15E148 Safari/604.1

Browser: Chrome Mobile iOS 85

Operating system: iOS 13.7

Device Platform: Mobile

Date tested: 4 years ago

Test name	Executions per second
for	995.1 Ops/sec
for (less closure)	975.5 Ops/sec
for of	2080.8 Ops/sec
for of (less closure)	1986.9 Ops/sec
forEach	1965.6 Ops/sec
forEach (less closure)	1914.9 Ops/sec
reduce	1912.4 Ops/sec
reduce (less closure)	1851.6 Ops/sec

Script Preparation code:

var array = [];
(function(theArray) {
  for (var i = 0, L = 10000; i < L; i += 1) {
    array.push({
      creationIndex: i,
      someStringifiedNumber: (Date.now() + '|' + Math.random())
    });
  }
})(array);
var result;

Tests:

for
var someValuesArray = []; for (var i = 0, L = array.length; i < L; i++) { var someVar = array[i]; var someValue = someVar.creationIndex + someVar.someStringifiedNumber; someValuesArray.push(someValue); } result = someValuesArray;
for (less closure)
var someValuesArray = []; var someVar; var someValue; for (var i = 0, L = array.length; i < L; i++) { someVar = array[i]; someValue = someVar.creationIndex + someVar.someStringifiedNumber; someValuesArray.push(someValue); } result = someValuesArray;
for of
var someValuesArray = []; for (var someVar of array) { var someValue = someVar.creationIndex + someVar.someStringifiedNumber; someValuesArray.push(someValue); } result = someValuesArray;
for of (less closure)
var someValuesArray = []; var someValue for (var someVar of array) { someValue = someVar.creationIndex + someVar.someStringifiedNumber; someValuesArray.push(someValue); } result = someValuesArray;
forEach
var someValuesArray = []; array.forEach(function(someVar) { var someValue = someVar.creationIndex + someVar.someStringifiedNumber; someValuesArray.push(someValue); }); result = someValuesArray;
forEach (less closure)
var someValuesArray = []; var someValue; array.forEach(function(someVar) { someValue = someVar.creationIndex + someVar.someStringifiedNumber; someValuesArray.push(someValue); }); result = someValuesArray;
reduce
var someValuesArray = array.reduce(function(valuesArray, someVar) { var someValue = someVar.creationIndex + someVar.someStringifiedNumber; valuesArray.push(someValue); return valuesArray; }, []); result = someValuesArray;
reduce (less closure)
var someValuesArray = []; var someValue; array.reduce(function(valuesArray, someVar) { someValue = someVar.creationIndex + someVar.someStringifiedNumber; valuesArray.push(someValue); return valuesArray; }, someValuesArray); result = someValuesArray;

Run results for: for, for of, forEach, and reduce. Each with and without reduced variable re-declarations.

Compare loop performance

for

for (less closure)

for of

for of (less closure)

forEach

forEach (less closure)

reduce

reduce (less closure)