Benchmark: slice vs length-1

Script Preparation code:

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

Tests:

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

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
`Array.slice`
`Array.length-1`

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 9 months ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/123.0.0.0 Safari/537.36

Browser/OS: Chrome 123 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
`Array.slice`	27681456.0 Ops/sec
`Array.length-1`	21536700.0 Ops/sec

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

LLMs can make mistakes. Check important info.

The provided JSON represents two microbenchmarks for measuring the performance of JavaScript arrays. The benchmarks compare two approaches to access the last element of an array: using `arr.slice(-1)` and `arr[arr.length - 1]`.

**Approaches Compared**

There are two main approaches being compared:

1. **`arr.slice(-1)`**: This method creates a new array containing only the last element of the original array. The `-1` index refers to the last element in the array.
2. **`arr[arr.length - 1]`**: This method directly accesses the last element of the array without creating a new array.

**Pros and Cons**

- **`arr.slice(-1)`**
	* Pros:
		+ Can be useful when you need to access only the last element of an array.
		+ Returns a new array, which can be more predictable in terms of performance.
	* Cons:
		+ Creates a new array, which may incur additional memory allocation and copying overhead.
		+ May have slower performance due to the creation of a new array.
- **`arr[arr.length - 1]`**
	* Pros:
		+ Directly accesses the last element without creating a new array.
		+ Typically faster and more efficient than `slice(-1)`.
	* Cons:
		+ May not be as predictable or safe to use, since it relies on the underlying internal representation of arrays.

**Library and Special JS Feature**

Neither of these approaches uses any specific JavaScript library. However, they do utilize a common JavaScript feature: array indexing. Both methods rely on the property access syntax `arr[index]` to access elements in an array.

**Other Considerations**

- **Optimization**: When optimizing performance-critical code, it's essential to consider the trade-offs between memory allocation and copying overhead vs. direct access to elements.
- **Predictability and Safety**: Using methods like `slice(-1)` can provide more predictable behavior and safety guarantees, especially when working with large arrays or in environments where array internal representations may vary.

**Alternative Approaches**

Other alternative approaches for accessing the last element of an array include:

- Using the `at()` method (introduced in ECMAScript 2019): `arr.at(-1)`
- Using a custom function to extract the last element, which can provide more control over performance and memory usage.

It's worth noting that these alternatives may not be supported by older browsers or JavaScript engines.

Related benchmarks:

slice vs length-1 (version: 0)

Comparing performance of: `Array.slice` vs `Array.length-1`

Created: 2 years ago by: Guest

Jump to the latest result

`Array.slice`

`Array.length-1`

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):