Run results for: for..in or keys+forEach

Run details:

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/66.0.3359.181 Safari/537.36

Browser: Chrome 66

Operating system: Mac OS X 10.13.0

Device Platform: Desktop

Date tested: 5 years ago

Test name	Executions per second
for..in	3158.6 Ops/sec
keys+forEach	3018.4 Ops/sec

Script Preparation code:

testObj = {};
for(let i = 0; i < 1000; i++) {
  testObj['a'+i] = i;
}

Tests:

for..in
let acc = 0; for (let k in testObj) { acc += testObj[k]; }
keys+forEach
let acc = 0; Object.keys(testObj).forEach((k) => { acc += testObj[k]; });