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

Run details:

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:135.0) Gecko/20100101 Firefox/135.0

Browser: Firefox 135

Operating system: Windows

Device Platform: Desktop

Date tested: one year ago

Benchmark engine: Benchmark.js

for in loop

19.8M/s

Object.assign

13.7M/s

View exact numbers

Test name	Executions per second
✓ for in loop	19,811,428 Ops/sec
Object.assign	13,673,039 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];