Benchmark: Speed of Arr.length and Slice

Script Preparation code:

var arr = [];
for (let i = 0; i < 1000000; i++) {
  arr.push(i);
}

Tests:

slice
arr.slice(-1)
arr.length
arr[arr.length-1]

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
slice
arr.length

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/112.0.0.0 Safari/537.36

Browser/OS: Chrome 112 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
slice	20647936.0 Ops/sec
arr.length	15768275.0 Ops/sec

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

LLMs can make mistakes. Check important info.

**Overview of the Benchmark**

The provided benchmark measures the speed of accessing elements at the end of an array in JavaScript, comparing two approaches: using `slice()` or directly indexing into the array (`arr.length-1`).

**Benchmark Definition**

The benchmark definition is represented by the JSON object:
```json
{
  "Name": "Speed of Arr.length and Slice",
  "Description": null,
  "Script Preparation Code": "var arr = [];\r\nfor (let i = 0; i < 1000000; i++) {\r\n  arr.push(i);\r\n}",
  "Html Preparation Code": null
}
```
This script creates an array of 1 million elements, then prepares for the benchmark by executing a loop that pushes elements onto the array.

**Individual Test Cases**

The benchmark consists of two test cases:
```json
[
  {
    "Benchmark Definition": "arr.slice(-1)",
    "Test Name": "slice"
  },
  {
    "Benchmark Definition": "arr[arr.length-1]",
    "Test Name": "arr.length"
  }
]
```
These test cases measure the execution time of accessing the last element in the array using two different methods:

1. `slice(-1)`: This method returns a new array containing the last element of the original array.
2. `arr[arr.length-1]`: This method directly accesses the element at the specified index, without creating a new array.

**Comparison of Approaches**

The pros and cons of each approach are:

* **`slice(-1)`:**
	+ Pros:
		- Creates a new array with the last element, which can be useful for specific use cases.
		- Can be faster in some browsers due to caching optimizations.
	+ Cons:
		- Creates an additional object in memory, increasing memory allocation and deallocation overhead.
		- May incur slower performance due to the creation of a new array.
* **`arr[arr.length-1]`:**
	+ Pros:
		- Directly accesses the element without creating a new array, reducing memory allocation and deallocation overhead.
		- Can be faster in some browsers due to caching optimizations for direct indexing.
	+ Cons:
		- May incur slower performance if the browser's caching mechanism is not optimized for this specific use case.

**Library/Feature Used**

The benchmark uses no external libraries or features. It relies solely on built-in JavaScript functionality.

**Other Considerations**

* The benchmark creates a large array of 1 million elements, which can impact memory allocation and deallocation overhead.
* The `slice(-1)` test case may incur slower performance due to the creation of an additional object in memory.
* The `arr[arr.length-1]` test case relies on direct indexing into the array, which may be faster but also more vulnerable to errors.

**Alternative Approaches**

Other approaches that could be tested in this benchmark include:

* Using `Array.prototype.at()` (available in ECMAScript 2020 and later):
```javascript
arr.at(-1)
```
This method returns a new view into the array, allowing for direct indexing without creating a new array.

* Using `Array.prototype.get()` (available in some browsers):
```javascript
arr.get(-1)
```
This method also allows for direct indexing into the array without creating a new array.

Note that these alternative approaches may not be supported by all browsers or versions of JavaScript.

Related benchmarks:

Speed of Arr.length and Slice (version: 0)

Comparing performance of: slice vs arr.length

Created: one year ago by: Guest

Jump to the latest result

slice

arr.length

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):