for-loop vs. for-in-loop (v8)

Revision 8 of this benchmark created by Javier López Pardo on

Description

Testing the speed of iterating various sized arrays with straight for-loop or with a for-in-loop over its keys.

Preparation HTML

<script>
  // setup `arr` array ('small')
  var arr = ['1', true, false, "", void 0, null, 2, 18.5936];

  // testing for having deleted keys in array
  delete(arr[3]);

  // seed `arr_keys` hash
  var arr_keys = {};
  for (var i = 0; i < arr.length; i++) {
    arr.hasOwnProperty(i) && (arr_keys[i] = 0);
  }

  // setup `arr2` array ('medium')
  var arr2 = arr.slice(0);
  for (var j = 0; j < 500; j++) {
    arr2.push(Math.round(Math.random()));
  }

  // seed `arr2_keys` hash
  var arr2_keys = {};
  for (j = 0; j < arr2.length; j++) {
    arr2.hasOwnProperty(j) && (arr2_keys[j] = 0);
  }

  // setup `arr3` array ('big')
  var arr3 = arr2.slice(0);
  for (var m = 0; m < 5000; m++) {
    arr3.push(Math.round(Math.random()));
  }

  // seed `arr3_keys` hash
  var arr3_keys = {};
  for (m = 0; m < arr3.length; m++) {
    arr3.hasOwnProperty(m) && (arr3_keys[m] = 0);
  }
</script>

Test runner

Ready to run.

Testing in
TestOps/sec
small array: for-loop
for (var i = 0, len = arr.length; i < len; i++) {
  arr[i];
}
ready
small array: for-in-loop on keys
for (var i in arr_keys) {
  arr[i];
}
ready
medium array: for-loop
for (var j = 0, len = arr2.length; j < len; j++) {
  arr2[j];
}
ready
medium array: for-in-loop on keys
for (var j in arr2_keys) {
  arr2[j];
}
ready
big array: for-loop
for (var m = 0, len = arr3.length; m < len; m++) {
  arr3[m];
}
ready
big array: for-in-loop on keys
for (var m in arr3_keys) {
  arr3[m];
}
ready
small array: native forEach
arr.forEach(function(item) {
  item;
});
ready
medium array: native forEach
arr2.forEach(function(item) {
  item;
});
ready
big array: native forEach
arr3.forEach(function(item) {
  item;
});
ready

Revisions

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