Run results for: JavaScript merge properties (huge object)

Run details:

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/119.0.0.0 Safari/537.36

Browser: Chrome 119

Operating system: Mac OS X 10.15.7

Device Platform: Desktop

Date tested: one year ago

Test name	Executions per second
Using the spread operator	1472.3 Ops/sec
Using Object.assign	1441.7 Ops/sec
Using assignment	2640.6 Ops/sec

Script Preparation code:

var propertyNames1 = Array.from({
    length: 1000
}).map((_, i) => `props${i}`)
var propertyNames2 = Array.from({
    length: 1000
}).map((_, i) => `props${i+1000}`)


var firstObject = {};

for (const propertyName of propertyNames1) {
    firstObject[propertyName] = propertyName;
}


var secondObject = {};

for (const propertyName of propertyNames2) {
    secondObject[propertyName] = propertyName;
}

Tests:

Using the spread operator
const finalObject = { ...firstObject, ...secondObject };
Using Object.assign
const finalObject = Object.assign({}, firstObject, secondObject);
Using assignment
const finalObject = {}; for (const key in firstObject) { finalObject[key] = firstObject[key]; } for (const key in secondObject) { finalObject[key] = secondObject[key]; }

Run results for: JavaScript merge properties (huge object)

Using the spread operator

Using Object.assign

Using assignment