Run results for: JavaScript spread operator vs Object.assign performance vs manual copy With more complex data

Run details:

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/132.0.0.0 Safari/537.36

Browser: Chrome 132

Operating system: Windows

Device Platform: Desktop

Date tested: one year ago

Manual copy

111.8M/s

Using the spread operator

20.1M/s

Using Object.assign

5.4M/s

View exact numbers

Test name	Executions per second
✓ Manual copy	111,812,960 Ops/sec
Using the spread operator	20,093,284 Ops/sec
Using Object.assign	5,357,952 Ops/sec

Script Preparation code:

const firstObject = {
    sampleData: 'Hello world',
    key1: 'value1',
    key2: 'value 2',
    key3: 'value 3',
    keyNum1: 123456
};
const secondObject = {
    moreData: 'foo bar',
    key1: 'value1.1',
    key4: 'value4'
};

Tests:

Using the spread operator
const finalObject = { ...firstObject, ...secondObject };
Using Object.assign
const finalObject = Object.assign({}, firstObject, secondObject);
Manual copy
const finalObject = { sampleData: firstObject.sampleData, key1 : firstObject.key1, key2 : firstObject.key2, key3 : firstObject.key3, keyNum1 : firstObject.keyNum1, moreData: secondObject.moreData , key1: secondObject.key1 , key4 : secondObject.key4 };