Run results for: Map vs For Loop vs For of vs For of entries

Run details:

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:109.0) Gecko/20100101 Firefox/115.0

Browser: Firefox 115

Operating system: Mac OS X 10.15

Device Platform: Desktop

Date tested: one year ago

Test name	Executions per second
Map	170.0 Ops/sec
For Loop	321.1 Ops/sec
foreach	306.8 Ops/sec
pre-allocated for loop	320.2 Ops/sec
pre-allocated unrolled for loop	324.9 Ops/sec
For of	159.0 Ops/sec
For of entries	68.0 Ops/sec

Script Preparation code:

var a = [];
for (var i = 0; i < 1e6; i++) {
  a[i] = Math.random();
}

Tests:

Map
var b = a.map(n => n * 2);
For Loop
var b = []; for (var i = 0; i < a.length; i++) { b[i] = a[i] * 2; }
foreach
var b = a.forEach(n => n * 2);
pre-allocated for loop
var b = new Array(a.length); for (var i = 0; i < a.length; i++) { b[i] = a[i] * 2; }
pre-allocated unrolled for loop
var b = new Array(a.length); for (var i = 0; i < a.length/4; i++) { b[i*4] = a[i*4] * 2; b[i*4+1] = a[i*4+1] * 2; b[i*4+2] = a[i*4+2] * 2; b[i*4+3] = a[i*4+3] * 2; }
For of
var b = [] for (var v of a) { b.push(v * 2) }
For of entries
var b = [] for (var [i, v] of a.entries()) { b[i] = v * 2 }