Benchmark: assign vs spread test inside loop

Tests:

assign
const a = { title: 'asd' } for (let i = 0; i < 1000; i++) { Object.assign(a, {[i]: i}) }
spread
let a = { title: 'asd' }; for (let i = 0; i < 1000; i++) { a = { ...a, [i]: i } }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
assign
spread

Fastest: N/A

Slowest: N/A

Latest run results:

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

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/124.0.0.0 Safari/537.36

Browser/OS: Chrome 124 on Windows

View result in a separate tab

Test name	Executions per second
assign	490.4 Ops/sec
spread	2987.2 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's break down the provided benchmark.

**What is being tested?**

The benchmark measures the performance difference between two approaches:

1. **`Object.assign()`**: This method copies properties from one or more source objects to a target object.
2. **Spread syntax (`...a, [i]: i`)**: This syntax creates a new object by copying all own enumerable properties from an existing object.

**Options compared**

The benchmark compares the performance of these two approaches inside a loop:

* Loop iteration: 1000 times
* Target object `a`: initialized with a single property `title`

**Pros and Cons**

1. **`Object.assign()`**:
	* Pros:
		+ Widely supported and well-maintained.
		+ Can handle multiple source objects.
	* Cons:
		+ May incur additional overhead due to method call and object creation.
2. **Spread syntax (`...a, [i]: i`)**:
	* Pros:
		+ More concise and expressive.
		+ Can be faster for simple assignments (e.g., assigning a single property).
	* Cons:
		+ Less widely supported (older browsers) or may require polyfills.
		+ Can lead to slower performance if used with complex objects or multiple properties.

**Other considerations**

* **Memory allocation**: Both approaches allocate memory for the target object and its properties. However, `Object.assign()` might allocate more memory due to additional overhead.
* **Type coercion**: Spread syntax can lead to type coercion when assigning values to properties (e.g., `i` is a number, but `[i]` is a string). This might impact performance in certain scenarios.

**Library and special JS feature**

There are no specific libraries used in this benchmark. However, the spread syntax (`...a, [i]: i`) relies on JavaScript's built-in syntax for object spread.

**Test user considerations**

When running this benchmark, users should consider the following:

* Older browsers may not support the spread syntax, which could impact performance and accuracy.
* The benchmark measures the execution rate (executions per second), so users might want to run multiple iterations to get a more accurate result.

**Alternatives**

Other alternatives for handling object assignments in JavaScript include:

1. **`Object.create()`**: Creates a new object with the specified prototype chain.
2. **`Object.init()`**: Initializes an object with the given properties (less widely supported).
3. **Manual property assignment**: Assigning properties individually using `a[i] = i;`.

These alternatives might offer different trade-offs in terms of performance, readability, and maintainability.

If you have any further questions or need more context, feel free to ask!

Related benchmarks:

assign vs spread test inside loop (version: 1)

Comparing performance of: assign vs spread

Created: 2 years ago by: Registered User

Jump to the latest result

assign

spread

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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