Run results for: JavaScript spread operator vs Object.assign vs for-in loop safe performance

Run details:

User agent: Mozilla/5.0 (iPhone; CPU iPhone OS 16_7 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) CriOS/122.0.6261.62 Mobile/15E148 Safari/604.1

Browser: Chrome Mobile iOS 122

Operating system: iOS 16.7

Device Platform: Mobile

Date tested: 2 years ago

Test name	Executions per second
✓ Using For-In loop	20,671,616 Ops/sec
Using the spread operator	9,263,728 Ops/sec
Using Object.assign	3,761,126 Ops/sec
Using For-In loop with hasOwnProperty	2,368,874 Ops/sec

Tests:

Using the spread operator
const firstObject = { sampleData: 'Hello world' } const secondObject = { moreData: 'foo bar' } const finalObject = { ...firstObject, ...secondObject };
Using Object.assign
const firstObject = { sampleData: 'Hello world' } const secondObject = { moreData: 'foo bar' } const finalObject = Object.assign({}, firstObject, secondObject);
Using For-In loop
const firstObject = { sampleData: 'Hello world' } const secondObject = { moreData: 'foo bar' } const finalObject = {} for (let key in firstObject) { finalObject[key] = firstObject[key]; } for (let key in secondObject) { finalObject[key] = secondObject[key]; }
Using For-In loop with hasOwnProperty
const firstObject = { sampleData: 'Hello world' } const secondObject = { moreData: 'foo bar' } const finalObject = {} for (let key in firstObject) { if (Object.prototype.hasOwnProperty.call(firstObject, key)) { finalObject[key] = firstObject[key]; } } for (let key in secondObject) { if (Object.prototype.hasOwnProperty.call(secondObject, key)) { finalObject[key] = secondObject[key]; } }

Run results for: JavaScript spread operator vs Object.assign vs for-in loop safe performance

Measure the fastest way to merge objects, without mutation.

Using the spread operator

Using Object.assign

Using For-In loop

Using For-In loop with hasOwnProperty