Benchmark: JavaScript spread operator vs Object.assign performance (Fair case)

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);

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

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

LLMs can make mistakes. Check important info.

Let's break down what's being tested in this JavaScript microbenchmark.

**What is being tested?**

The benchmark measures the performance difference between two approaches: using the spread operator (`...`) and `Object.assign` to merge two objects into a new object.

**Options compared:**

* **Using the spread operator (`...`)**: This approach uses the spread operator to expand the properties of an object. The syntax is `const finalObject = { ...firstObject, ...secondObject };`. This creates a shallow copy of both objects and merges their properties into a new object.
* **Using Object.assign**: This approach uses the `Object.assign` method to merge two objects. The syntax is `const finalObject = Object.assign({}, firstObject, secondObject);`. This also creates a shallow copy of both objects and merges their properties into a new object.

**Pros and Cons:**

* **Using the spread operator (`...`)**:
	+ Pros:
		- More concise and expressive code
		- Allows for more flexible merging of objects (e.g., using `Object.assign()` with a custom object as the target)
	+ Cons:
		- May be slower due to the overhead of creating a new array-like object
* **Using Object.assign**:
	+ Pros:
		- Faster than the spread operator approach, since it doesn't create a new object or array-like structure
	+ Cons:
		- Less concise and expressive code
		- May not be as flexible as the spread operator approach

**Library:**

There is no explicit library being used in this benchmark. However, `Object.assign` is a built-in method in JavaScript.

**Special JS feature or syntax:**

* **Spread operator (`...`)**: This was introduced in ECMAScript 2015 (ES6) as a new way to create objects and arrays. It allows for more concise and expressive code when working with objects and arrays.

Now, let's talk about alternatives:

Other ways to merge objects in JavaScript include using the `lodash.merge` function from the Lodash library or creating a custom merging function using loops and conditional statements. However, these approaches may not be as efficient as using the spread operator or `Object.assign`.

Here's an example of how you could implement a custom merging function:
```javascript
function mergeObjects(firstObject, secondObject) {
  const result = {};
  for (const key in firstObject) {
    if (key in secondObject) {
      result[key] = firstObject[key];
    } else {
      result[key] = firstObject[key];
    }
  }
  for (const key in secondObject) {
    if (!(key in result)) {
      result[key] = secondObject[key];
    }
  }
  return result;
}
```
This function creates a shallow copy of the `firstObject` and then iterates through the properties of both objects, merging them into a new object. However, this approach is less concise and expressive than using the spread operator or `Object.assign`.

Latest run results:

Run details: (Test run date: 3 years ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:86.0) Gecko/20100101 Firefox/86.0

Browser/OS: Firefox 86 on Mac OS X 10.14

View result in a separate tab

Test name	Executions per second
Using the spread operator	4725896.0 Ops/sec
Using Object.assign	4731810.0 Ops/sec

Related benchmarks:

JavaScript spread operator vs Object.assign performance (Fair case) (version: 0)

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

Created: 3 years ago by: Guest

Jump to the latest result

Using the spread operator

Using Object.assign

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

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