Benchmark: JavaScript spread operator vs Object.assign performance reassign same variable

Tests:

Using the spread operator
let firstObject = { sampleData: 'Hello world' } const secondObject = { moreData: 'foo bar' } firstObject = {...firstObject, ...secondObject}
Using Object.assign
const firstObject = { sampleData: 'Hello world' } const secondObject = { moreData: 'foo bar' } Object.assign(firstObject, secondObject);

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Using the spread operator
Using Object.assign

Fastest: N/A

Slowest: N/A

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/121.0.0.0 Safari/537.36

Browser/OS: Chrome 121 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
Using the spread operator	26536946.0 Ops/sec
Using Object.assign	10592839.0 Ops/sec

Autogenerated LLM Summary (model llama3.2:3b, generated one year ago):

LLMs can make mistakes. Check important info.

Let's dive into the world of JavaScript microbenchmarks!

**Benchmark Overview**

The provided JSON represents a benchmark test case for measuring the performance difference between two approaches: using the spread operator (`...`) and `Object.assign()` to merge two objects.

**Options Compared**

Two options are being compared:

1. **Using the spread operator**: This approach uses the syntax `{...firstObject, ...secondObject}` to create a new object that combines the properties of `firstObject` and `secondObject`. The spread operator (`...`) is used to expand the elements of an array or object.
2. **Using `Object.assign()`**: This approach uses the `Object.assign()` method to merge two objects into one.

**Pros and Cons of Each Approach**

* **Using the spread operator:**
	+ Pros:
		- Can be more concise and expressive than using `Object.assign()`.
		- May be faster since it doesn't require a function call.
	+ Cons:
		- Requires JavaScript version 4 or later, as older versions don't support the spread operator.
		- Can be slower for very large objects due to the creation of multiple temporary objects.
* **Using `Object.assign()`**:
	+ Pros:
		- More widely supported across different browsers and JavaScript versions (since it's a built-in method).
		- Generally faster since it uses a native implementation.
	+ Cons:
		- Can be less concise than using the spread operator.

**Library Used**

In this benchmark, no specific library is used beyond the standard JavaScript methods (`Object.assign()`).

**Special JS Feature/Syntax**

The use of the spread operator (`...`) is a relatively recent feature introduced in ECMAScript 2018. It allows for more concise and expressive object merging and array expansion.

**Other Considerations**

When benchmarking these two approaches, it's essential to consider factors like:

* The size and complexity of the objects being merged.
* The browser version and platform being tested.
* The presence of other scripts or dependencies that might affect performance.

**Alternative Approaches**

If you're interested in exploring alternative methods for merging objects, here are a few options:

1. **`.concat()`**: This method involves concatenating two arrays using the `Array.prototype.concat()` method, which can be slower than `Object.assign()`.
2. **`reduce()`**: You can use the `Array.prototype.reduce()` method to merge two arrays by accumulating the results.
3. **Custom implementation**: You can implement your own custom function for merging objects, which might provide better performance but requires more effort.

Keep in mind that these alternatives may not be as widely supported or optimized as using `Object.assign()`.

Related benchmarks:

JavaScript spread operator vs Object.assign performance reassign same variable (version: 0)

Comparing performance of: Using the spread operator vs Using Object.assign

Created: 7 years ago by: Guest

Jump to the latest result

Using the spread operator

Using Object.assign

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated one year ago):