Benchmark: object.assign vs spread operator for shallow copying large objects 2

Script Preparation code:

var a={};
var i=10000;
while(i--)a[i]=i;

Tests:

var copy={...a}
var copy={...a}
var copy = Object.assign({}, a)
var copy = Object.assign({}, a)

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
var copy={...a}
var copy = Object.assign({}, a)

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: one year ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/16.4 Safari/605.1.15

Browser/OS: Safari 16 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
var copy={...a}	582.3 Ops/sec
var copy = Object.assign({}, a)	540.7 Ops/sec

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

LLMs can make mistakes. Check important info.

I'll break down the benchmark definition and test cases to explain what's being tested, compared, and their pros and cons.

**Benchmark Definition**

The benchmark is designed to compare two approaches for shallow copying large objects:

1. **Spread operator (`...a`)**
2. **`Object.assign()` method**

**Script Preparation Code**

The script preparation code creates a large object `a` with 10,000 properties, where each property is assigned a value equal to its index (e.g., `a[0] = 0`, `a[1] = 1`, etc.). This helps to create a large, dense object that requires shallow copying.

**Html Preparation Code**

The html preparation code is empty, which means no additional HTML context or setup is required for the benchmark.

**Individual Test Cases**

There are two test cases:

1. **Test Case 1: `var copy = {...a}`**

This test case uses the spread operator to create a shallow copy of object `a`. The syntax `{...a}` creates a new object and copies the properties from `a` into it using the spread operator.

2. **Test Case 2: `var copy = Object.assign({}, a)`**

This test case uses the `Object.assign()` method to create a shallow copy of object `a`. The syntax `Object.assign(copy, a)` creates a new object and copies the properties from `a` into it using the `Object.assign()` method.

**Pros and Cons**

Here's a brief summary of the pros and cons of each approach:

1. **Spread Operator (`...a`)**
	* Pros:
		+ More concise and expressive syntax
		+ Can be used to create new objects in a more declarative way
	* Cons:
		+ May not work as expected with complex or deeply nested objects
		+ Can lead to unexpected behavior if not used carefully (e.g., modifying the original object)
2. **`Object.assign()` method**
	* Pros:
		+ More predictable and robust behavior
		+ Works well with complex or deeply nested objects
	* Cons:
		+ More verbose syntax compared to the spread operator
		+ May require additional setup (e.g., creating an empty target object)

**Library and Special JS Feature**

Neither of these test cases uses any external libraries. However, they do demonstrate a specific JavaScript feature:

* The spread operator (`...a`) is a relatively new addition to the JavaScript language, introduced in ECMAScript 2018.
* The `Object.assign()` method has been part of the JavaScript language since its inception.

**Other Alternatives**

If you're looking for alternative approaches to shallow copying objects, here are some options:

1. **`JSON.parse(JSON.stringify(a))`**: This method uses the `JSON.parse()` and `JSON.stringify()` functions to create a deep copy of an object.
2. **`Object.create(null)`**: This method creates a new object with no prototype chain, which can be used as a shallow copy.
3. **`Array.prototype.slice.call(a)`**: This method creates a new array from the properties of an object.

Keep in mind that each approach has its own trade-offs and use cases. The spread operator and `Object.assign()` method are generally recommended for shallow copying objects, while other methods may be more suitable for deeper or more complex copies.

Related benchmarks:

object.assign vs spread operator for shallow copying large objects 2 (version: 0)

spread operator vs object.assign

Comparing performance of: var copy={...a} vs var copy = Object.assign({}, a)

Created: 2 years ago by: Guest

Jump to the latest result

var copy={...a}

var copy = Object.assign({}, a)

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

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