Benchmark: `Array.slice(-1)[0]` vs `Array[Array.length]`

Script Preparation code:

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

Tests:

`Array.slice(-1)[0]`
arr.slice(-1)[0];
`Array[Array.length]`
arr[arr.length-1];

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
`Array.slice(-1)[0]`
`Array[Array.length]`

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 4 years ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_3) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/81.0.4044.129 Safari/537.36

Browser/OS: Chrome 81 on Mac OS X 10.15.3

View result in a separate tab

Test name	Executions per second
`Array.slice(-1)[0]`	10328980.0 Ops/sec
`Array[Array.length]`	7843144.0 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, compared, and analyzed.

**Benchmark Overview**

The benchmark is comparing two ways to access the last element of an array in JavaScript: `Array.slice(-1)[0]` and `arr[arr.length-1]`.

**Script Preparation Code**

Before running each test case, the script preparation code creates a large array (`arr`) with 100 elements, using the following line:
```javascript
var arr = Array.from(Array(100).keys());
```
This creates an array of numbers from 0 to 99.

**Benchmark Definition**

The benchmark definition is a JSON object that contains two test cases:

1. `Array.slice(-1)[0];`: This test case measures the performance of accessing the last element of the array using the `slice()` method and indexing `[0]`.
2. `arr[arr.length-1];`: This test case measures the performance of accessing the last element of the array directly using indexing `[arr.length-1]`.

**Library/Features Used**

In this benchmark, no libraries or special JavaScript features are used.

**Options Compared**

The two options being compared are:

1. Using `Array.slice(-1)[0]`: This method creates a new slice of the original array with only one element (the last one), and then accesses that element using `[0]`. This approach is often considered more explicit and safer, but may incur a performance overhead due to the creation of a new slice.
2. Using `arr[arr.length-1]`: This method directly indexes into the original array to access the last element. This approach is often considered faster and more efficient, as it avoids creating unnecessary intermediate data structures.

**Pros and Cons**

Here are some pros and cons of each approach:

* **Using `Array.slice(-1)[0]`**:
	+ Pros: More explicit and safer, as it avoids modifying the original array.
	+ Cons: May incur a performance overhead due to the creation of a new slice.
* **Using `arr[arr.length-1]`**:
	+ Pros: Faster and more efficient, as it directly indexes into the original array.
	+ Cons: Less explicit and safer, as it relies on indexing into the array.

**Other Alternatives**

If you need to access the last element of an array in JavaScript, other alternatives include:

* Using `arr[arr.length - 1]`: This is a more concise way to access the last element using direct indexing.
* Using a library like Lodash, which provides a function called `last()` that can be used to access the last element of an array.

**Benchmark Result**

The latest benchmark result shows the performance metrics for both test cases:

| Test Name | ExecutionsPerSecond |
| --- | --- |
| `Array.slice(-1)[0]` | 10328980.0 |
| `arr[arr.length-1]` | 7843144.0 |

This suggests that accessing the last element using `arr[arr.length-1]` is faster than using `Array.slice(-1)[0]`. However, the actual performance difference may vary depending on the specific use case and JavaScript engine being used.

I hope this explanation helps!

Related benchmarks:

`Array.slice(-1)[0]` vs `Array[Array.length]` (version: 0)

Comparing performance of: `Array.slice(-1)[0]` vs `Array[Array.length]`

Created: 4 years ago by: Guest

Jump to the latest result

`Array.slice(-1)[0]`

`Array[Array.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):