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

Run details:

User agent: Mozilla/5.0 (iPhone; CPU iPhone OS 18_5 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/18.5 Mobile/15E148 Safari/604.1

Browser: Mobile Safari 18

Operating system: iOS 18.5

Device Platform: Mobile

Date tested: one year ago

Benchmark engine: Benchmark.js

for in loop

14.8M/s

Object.assign

7.4M/s

View exact numbers

Test name	Executions per second
✓ for in loop	14,806,800 Ops/sec
Object.assign	7,393,674 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];