Benchmark: `Array.slice(0, N)` vs `Array.length = N` sd4343

Script Preparation code:

var arr = ["1","2","3","4","5","6","7","8","9","10","11","12","13","14","15","16","17","18","19","20","21","22"];

Tests:

`Array.slice(0, N)`
arr.slice(0, 20);
`Array.length = N`
arr.length = 20;

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
`Array.slice(0, N)`
`Array.length = N`

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/537.36 (KHTML, like Gecko) Chrome/110.0.0.0 Safari/537.36

Browser/OS: Chrome 110 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
`Array.slice(0, N)`	17795338.0 Ops/sec
`Array.length = N`	14467937.0 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's break down the provided benchmark and explain what's being tested.

**Overview**

The benchmark compares two approaches for creating an array with a fixed length in JavaScript:

1. `arr.slice(0, N)` (without assigning to a variable)
2. `arr.length = N` (assigning a value to the `length` property)

**Options Compared**

Both approaches create an array with 20 elements initialized with numbers from 1 to 20.

* Option 1: `arr.slice(0, 20)` creates a new array and copies the first 20 elements of the original array (`var arr = [...]`) into it. The `slice` method returns a shallow copy of the specified portion of an array.
* Option 2: `arr.length = N` assigns a value to the `length` property, but does not create any actual array elements. This approach only sets the length of the array without populating it.

**Pros and Cons**

* **Option 1 (Array slicing)**:
	+ Pros: creates an actual array with elements, which can be used in further operations.
	+ Cons: may incur additional memory allocation and copying overhead due to creating a new array.
* **Option 2 (Assigning `length` property)**:
	+ Pros: faster and more lightweight, as it only sets the length without creating any elements.
	+ Cons: does not create an actual array with elements, which may limit its usefulness.

**Library**

None of the provided benchmark uses a library. However, if you're using modern JavaScript features like `Array.from()` or `Array.prototype.fill()`, they might be used in other benchmarks.

**Special JS Feature/Syntax (Not Applicable)**

Since neither test case uses any special JavaScript features or syntax, there's nothing to explain here.

**Other Alternatives**

Alternative approaches for creating arrays with a fixed length include:

* Using the spread operator (`[...Array(N)]`): creates an array filled with `N` elements.
* Using `Array(N)`: creates an array filled with `N` elements (this is similar to Option 2, but the `length` property is not set directly).
* Using a loop: creates an array by iterating over a range of numbers and assigning each one to an element.

Keep in mind that these alternatives might have different performance characteristics depending on the specific use case.

Related benchmarks:

`Array.slice(0, N)` vs `Array.length = N` sd4343 (version: 0)

Comparing performance of: `Array.slice(0, N)` vs `Array.length = N`

Created: one year ago by: Guest

Jump to the latest result

`Array.slice(0, N)`

`Array.length = N`

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):