Benchmark: JavaScript spread operator vs Object.assign vs null-checked for-in loop performance

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 type checks
const firstObject = { sampleData: 'Hello world' } const secondObject = { moreData: 'foo bar' } const finalObject = {} if (firstObject != null) { for (let key in firstObject) { if (Object.prototype.hasOwnProperty.call(firstObject, key)) { finalObject[key] = firstObject[key]; } } } if (secondObject != null) { for (let key in secondObject) { if (Object.prototype.hasOwnProperty.call(secondObject, key)) { finalObject[key] = secondObject[key]; } } }

Rendered benchmark preparation results:

Previous results

Test case name	Result
Using the spread operator
Using Object.assign
Using For-In loop
Using For-In loop with type checks

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Latest run results:

Run details: (Test run date: 2 years ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/96.0.4664.110 Safari/537.36

Browser/OS: Chrome 96 on Mac OS X 10.15.7

Test name	Executions per second
Using the spread operator	5106751.0 Ops/sec
Using Object.assign	10110170.0 Ops/sec
Using For-In loop	74083860.0 Ops/sec
Using For-In loop with type checks	5852321.0 Ops/sec

JavaScript spread operator vs Object.assign vs null-checked for-in loop performance (version: 0)