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

Script Preparation code:

var arr = Array.from(Array(100).keys());

Tests:

`Array.slice(0, N)`
arr.slice(0, 20);
`Array.length = N`
arr.length = 20;
`Object.assign([], arr)` with `Array.length = N`
var newArr = Object.assign([], arr); newArr.length = 20;

Historical Performance Data aggregated from 22 community runs

Desktop Results:

Chrome 22 runs

`Array.slice(0, N)`

12.8M/s

`Array.length = N`

10.9M/s

`Object.assign([], arr)` with `Array.length = N`

296K/s

Fastest: `Array.slice(0, N)` (43.1x faster)

View exact numbers

✓ `Array.slice(0, N)`: 12,772,138 ops/sec
• `Array.length = N`: 10,928,885 ops/sec
• `Object.assign([], arr)` with `Array.length = N`: 296,281 ops/sec

Results show median performance across all community submissions. Run this benchmark yourself to verify on your device.

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
`Array.slice(0, N)`
`Array.length = N`
`Object.assign([], arr)` with `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 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/137.0.0.0 Safari/537.36

Browser/OS: Chrome 137 on Windows

View result in a separate tab

`Array.slice(0, N)`

23.6M/s

`Array.length = N`

20.4M/s

`Object.assign([], arr)` with `Array.length = N`

231K/s

View exact numbers

Test name	Executions per second
✓ `Array.slice(0, N)`	23,557,978 Ops/sec
`Array.length = N`	20,357,434 Ops/sec
`Object.assign([], arr)` with `Array.length = N`	231,196 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 benchmark and explain what's being tested.

**Benchmark Definition**

The benchmark is defined in JSON format, which represents a comparison between three different approaches to set the length of an array:

1. `Array.slice(0, N)` - This approach creates a new array by slicing the original array from index 0 to the specified length (N).
2. `Array.length = N` - This approach directly sets the length property of the original array.
3. `Object.assign([], arr) with Array.length = N` - This approach uses the `Object.assign()` method to create a new object from an empty array and then assigns the desired length to the resulting array.

**Options Compared**

The benchmark compares these three approaches in terms of their performance, specifically:

* Execution speed
* Number of executions per second

**Pros and Cons of Each Approach**

1. **`Array.slice(0, N)`**:
	* Pros: Creates a new array with the desired length, which can be useful for certain use cases.
	* Cons: May incur additional overhead due to creating a new array object, which can lead to slower performance compared to direct property assignment.
2. **`Array.length = N`**:
	* Pros: Directly sets the length property of the original array, which is likely to be faster since it doesn't involve creating a new object or array.
	* Cons: Can lead to issues if the length is set incorrectly, as it will affect all elements in the array.
3. **`Object.assign([], arr) with Array.length = N`**:
	* Pros: Uses a more functional programming approach, which can be beneficial for some use cases.
	* Cons: Creates an unnecessary intermediate object and assigns its length to the resulting array, adding overhead.

**Library Usage**

None of the benchmarked approaches rely on external libraries. The `Array` object is used directly in each case.

**Special JS Feature/Syntax**

None of the benchmarked approaches utilize special JavaScript features or syntax beyond standard language constructs.

**Other Alternatives**

If you need to set an array length, alternative approaches could include:

* Using a library like Lodash, which provides a `_.setLength()` function.
* Utilizing a specialized data structure, such as a sparse array, which can be created using `Array.prototype.set()` or similar methods.
* Implementing a custom length setter using a closure or a proxy object.

Keep in mind that the choice of approach depends on the specific use case and performance requirements. The benchmark results provided by MeasureThat.net can help inform these decisions.

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

Comparing performance of: `Array.slice(0, N)` vs `Array.length = N` vs `Object.assign([], arr)` with `Array.length = N`

Created: 6 years ago by: Guest

Go to the latest result

`Array.slice(0, N)`

`Array.length = N`

`Object.assign([], arr)` with `Array.length = N`

Historical Performance Data aggregated from 22 community runs

Desktop Results:

Chrome 22 runs

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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

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

Comparing performance of: `Array.slice(0, N)` vs `Array.length = N` vs `Object.assign([], arr)` with `Array.length = N`

Created: 6 years ago by: Guest

Go to the latest result

`Array.slice(0, N)`

`Array.length = N`

`Object.assign([], arr)` with `Array.length = N`

Historical Performance Data aggregated from 22 community runs

Desktop Results:

Chrome 22 runs

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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

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