Run results for: Reading array length inside vs outside for loop

Run details:

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36

Browser: Chrome 120

Operating system: Mac OS X 10.15.7

Device Platform: Desktop

Date tested: 2 years ago

reading length outside the for loop

34K/s

reading length inside the for loop

362/s

View exact numbers

Test name	Executions per second
✓ reading length outside the for loop	34,463 Ops/sec
reading length inside the for loop	362 Ops/sec

Script Preparation code:

var arr = [];
var i = 0;

while (i <= 1E5) arr[i] = i++;

Tests:

reading length outside the for loop
const length = arr.length for(var i = 0; i < length; i++) {}
reading length inside the for loop
for(var i = 0; i < arr.length; i++) {}