Run results for: Object iteration vs Map iteration

Run details:

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/135.0.0.0 Safari/537.36

Browser: Chrome 135

Operating system: Windows

Device Platform: Desktop

Date tested: one year ago

Object - for in

13.8M/s

Map - for of kv

6.0M/s

Map - forEach

4.3M/s

Object.entries() - for of kv

1.1M/s

Object.entries() - forEach

249K/s

View exact numbers

Test name	Executions per second
✓ Object - for in	13,777,459 Ops/sec
Map - for of kv	5,979,305 Ops/sec
Map - forEach	4,283,945 Ops/sec
Object.entries() - for of kv	1,111,640 Ops/sec
Object.entries() - forEach	248,945 Ops/sec

Script Preparation code:

var obj = {
  a: 1,
  b: 2,
  c: 3,
  d: 4,
  e: 5,
  f: 6,
  g: 7,
  h: 8,
  i: 9,
  j: 10,
  k: 11,
  l: 12,
  m: 13,
  n: 14,
  o: 15,
  p: 16,
  q: 17,
  r: 18,
  s: 19,
  t: 20,
  u: 21,
  v: 22,
  w: 23,
  x: 24,
  y: 25,
  z: 26
};
var map = new Map(Object.entries(obj));

Tests:

Map - for of kv
let total = 0; for (const [key, value] of map) { total += value; }
Map - forEach
let total = 0; map.forEach(function(value, key) { total += value; });
Object.entries() - for of kv
let total = 0; for (const [key, value] of Object.entries(obj)) { total += value; }
Object.entries() - forEach
let total = 0; Object.entries(obj).forEach(function(value, key) { total += value; });
Object - for in
let total = 0; for (const key in obj) { total += obj[key]; }