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

Test name	Executions per second
✓ Using For-In loop	41,620,304 Ops/sec
Using Object.assign	22,564,900 Ops/sec
Using For-In loop with hasOwnProperty	21,270,180 Ops/sec
Using the spread operator	13,133,539 Ops/sec

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