Run results for: Loop Optimization

Run details:

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/64.0.3282.140 Safari/537.36

Browser: Chrome 64

Operating system: Windows

Device Platform: Other

Date tested: 2025 years ago

Test name	Executions per second
For loop, basic	1792.4 Ops/sec
While loop, basic	1868.5 Ops/sec
For loop, cached (inside for statement)	2771.5 Ops/sec
For loop, cached (outside for statement)	2846.3 Ops/sec
For loop, i-- (caching inside for loop)	2884.0 Ops/sec
For loop, i-- (caching outside for loop)	2297.7 Ops/sec
While loop, cached	2607.3 Ops/sec
While loop, i--	2628.4 Ops/sec
forEach	6036.7 Ops/sec

Script Preparation code:

  var arr = [];
  for (var i = 0; i < 1000; i++) {
    arr[i] = i;
  }

  function someFn(ix) {
    return ix * 5 + 1 / 3 * 8;
  }

Tests:

For loop, basic
for (var i = 0; i < arr.length; i++) { someFn(arr[i]); }
While loop, basic
var i = 0; while (i < arr.length) { someFn(arr[i]); i++; }
For loop, cached (inside for statement)
for (var i = 0, len = arr.length; i < len; i++) { someFn(arr[i]); }
For loop, cached (outside for statement)
var len = arr.length; for (var i = 0; i < len; i++) { someFn(arr[i]); }
For loop, i-- (caching inside for loop)
for (var i = arr.length; i > 0; i--) { someFn(arr[i]); }
For loop, i-- (caching outside for loop)
var i = arr.length; for (; i--;) { someFn(arr[i]); }
While loop, cached
var len = arr.length; var i = 0; while(i < len){ someFn(arr[i]); i++; }
While loop, i--
var i = arr.length; while(i--){ someFn(arr[i]); }
forEach
arr.forEach(function(arrI){ someFn(arrI); });