Benchmark: Array Slice vs index

Script Preparation code:

var x = [...Array(1000).keys()]

function getIndexLast(a) { return a[a.length-1]}
function getSliceLast(a) { return a.slice(-1)[0]}

Tests:

getIndexLast
getIndexLast(x)
getSliceLast
getSliceLast(x)

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
getIndexLast
getSliceLast

Fastest: N/A

Slowest: N/A

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

LLMs can make mistakes. Check important info.

Let's break down the provided benchmark and explain what's being tested, compared, and the pros/cons of each approach.

**Benchmark Definition**

The benchmark is designed to measure the performance difference between two approaches: accessing an array element using its index (`getIndexLast`) versus slicing the array from the end (`getSliceLast`).

**Script Preparation Code**

The script preparation code creates a large array `x` with 1000 elements, and then defines two functions:

* `getIndexLast(a)`: This function takes an array `a` as input and returns the last element of the array using its index. In JavaScript, arrays are zero-based, so the last element is accessed at `a[a.length-1]`.
* `getSliceLast(a)`: This function also takes an array `a` as input but uses the `slice()` method to get a new array containing only the last element of `a`. The `-1` index in `slice(-1)` tells JavaScript to start from the end of the array and extract one element.

**Html Preparation Code**

The HTML preparation code is empty, which means that the benchmark doesn't generate any HTML content that would affect the test outcome. This is likely because the focus is on measuring the performance difference between the two array access methods.

**Individual Test Cases**

There are two test cases:

* `getIndexLast(x)`: This test case measures the performance of accessing an array element using its index.
* `getSliceLast(x)`: This test case measures the performance of slicing an array from the end to get a single element.

**Library and Purpose**

The library used in this benchmark is not explicitly mentioned, but it's likely that the JavaScript engine being tested (e.g., V8 in Chrome) provides the necessary implementation for these functions. The purpose of using libraries like this is to isolate the performance difference between the two array access methods and focus on the JavaScript engine's optimization.

**Special JS Feature or Syntax**

There are no special JavaScript features or syntax used in this benchmark beyond what's standard for accessing arrays.

**Pros/Cons of Each Approach**

* **getIndexLast(a)**:
	+ Pros: This approach is more readable, as it directly accesses the last element of the array using its index. It also avoids creating a new array.
	+ Cons: This approach may be slower due to the overhead of accessing an element by its index.
* **getSliceLast(a)**:
	+ Pros: This approach creates a new array containing only the last element, which can lead to better cache locality and potentially faster execution. However, it requires allocating memory for the new array.
	+ Cons: This approach is less readable than `getIndexLast(a)`, as it involves creating an intermediate result.

**Other Considerations**

* **Cache Locality**: When accessing an array element using its index (`getIndexLast(a)`), JavaScript may not be able to predict where in the cache the data will be located, leading to slower execution. In contrast, slicing an array from the end (`getSliceLast(a)`) can lead to better cache locality because the resulting array is contiguous.
* **Memory Allocation**: Creating a new array using `slice()` allocates memory for the new array, which may affect performance.

**Alternatives**

There are other alternatives to measure the performance difference between accessing an array element by its index and slicing an array from the end:

1. Using a different data structure, such as an object or a linked list.
2. Comparing the performance of using `at()` (a new feature in modern JavaScript) instead of `get` or indexing directly.
3. Benchmarking other operations, such as sorting or finding elements within an array.

Keep in mind that these alternatives may not provide the same level of insight into the performance characteristics of accessing arrays, but they can still help identify areas for optimization.

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/117.0.0.0 Safari/537.36

Browser/OS: Chrome 117 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
getIndexLast	18300452.0 Ops/sec
getSliceLast	14672304.0 Ops/sec

Related benchmarks:

Array Slice vs index (version: 0)

Comparing performance of: getIndexLast vs getSliceLast

Created: one year ago by: Guest

Jump to the latest result

getIndexLast

getSliceLast

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

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