Run results for: JavaScript spread operator vs Object.assign performance, large objects

Test name	Executions per second
✓ Using Object.assign (known change)	7,690 Ops/sec
Using the spread operator (known change)	7,257 Ops/sec
Using Object.assign	3,514 Ops/sec
Using the spread operator	2,243 Ops/sec

Using the spread operator

const firstObject = {}
const secondObject = {}

for(let i = 1; i < 1000; i++) firstObject[i] = Math.random();
for(let i = 1; i < 1000; i++) secondObject[i] = firstObject[i];

let rnd = Math.floor(Math.random() * 1000);
secondObject[rnd] = Math.random();

const finalObject = {
	...firstObject,
  	...secondObject
};

console.log("first", firstObject)
console.log("second", secondObject)
console.log("final", finalObject)

Using Object.assign

const firstObject = {}
const secondObject = {}

for(let i = 1; i < 1000; i++) firstObject[i] = Math.random();
for(let i = 1; i < 1000; i++) secondObject[i] = firstObject[i];

let rnd = Math.floor(Math.random() * 1000);
secondObject[rnd] = Math.random();

const finalObject = Object.assign(firstObject, secondObject);

console.log("first", firstObject)
console.log("second", secondObject)
console.log("final", finalObject)

Using Object.assign (known change)

const firstObject = {}
const secondObject = {}

for(let i = 1; i < 1000; i++) firstObject[i] = Math.random();
for(let i = 1; i < 1000; i++) secondObject[i] = firstObject[i];

let rnd = Math.floor(Math.random() * 1000);
secondObject[rnd] = Math.random();

let diff = {}
diff[rnd] = secondObject[rnd];

const finalObject = Object.assign(firstObject, diff);

console.log("first", firstObject)
console.log("second", secondObject)
console.log("final", finalObject)

Using the spread operator (known change)

const firstObject = {}
const secondObject = {}

for(let i = 1; i < 1000; i++) firstObject[i] = Math.random();
for(let i = 1; i < 1000; i++) secondObject[i] = firstObject[i];

let rnd = Math.floor(Math.random() * 1000);
secondObject[rnd] = Math.random();

let diff = {}
diff[rnd] = secondObject[rnd];

const finalObject = {
	...firstObject,
  	...diff
};

console.log("first", firstObject)
console.log("second", secondObject)
console.log("final", finalObject)

Run results for: JavaScript spread operator vs Object.assign performance, large objects

For large objects, 1 value change only

Using the spread operator

Using Object.assign

Using Object.assign (known change)

Using the spread operator (known change)