Run results for: JavaScript Object.assign vs for in loop

Run details:

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/18.1 Safari/605.1.15

Browser: Safari 18

Operating system: Mac OS X 10.15.7

Device Platform: Desktop

Date tested: one year ago

Benchmark engine: Benchmark.js

for in loop

34.5M/s

Object.assign

18.9M/s

View exact numbers

Test name	Executions per second
✓ for in loop	34,512,404 Ops/sec
Object.assign	18,863,658 Ops/sec

Tests:

Object.assign
const a = { x: 'xxx', y: 1, z: null } const b = { z: 1, u: 'uuu', v: null } Object.assign(a, b);
for in loop
const a = { x: 'xxx', y: 1, z: null } const b = { z: 1, u: 'uuu', v: null } for (let prop in b) a[prop] = b[prop];