Benchmark: Get last element of array2

Script Preparation code:


var arr = Array(100000000).fill(0);

Tests:

length
var a = arr[arr.length - 1];
at
var b = arr.at(-1);
slice
var c = arr.slice(-1)[0]

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
length
at
slice

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 2 years ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/125.0.0.0 Safari/537.36

Browser/OS: Chrome 125 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
length	5251306.5 Ops/sec
at	9310570.0 Ops/sec
slice	6900354.5 Ops/sec

Autogenerated LLM Summary (model gemma2:9b, generated one year ago):

LLMs can make mistakes. Check important info.

This benchmark on MeasureThat.net compares three different ways to access the last element of a very large array in JavaScript.  Let's break down each approach:

**1. `length`:** This method uses the `length` property of the array to get the index of the last element and then accesses that element directly.
   - **Code:** `var a = arr[arr.length - 1];`

* **Pros:**  This is often considered the most straightforward and intuitive way to access the last element. It's simple to understand and implement.
* **Cons:** In some situations, it can be slightly less performant than other methods, especially with very large arrays.

**2. `at()`:** The `at()` method allows you to access elements in an array by index, even negative indices.  `-1` refers to the last element.
   - **Code:** `var b = arr.at(-1);`

* **Pros:** Introduced in ECMAScript 2019, this method is often faster than using `length` and provides a more explicit way to access elements by index.  
* **Cons:** Not all JavaScript environments support it as it's relatively new. If you need wide browser compatibility, consider alternative methods.

**3. `slice()`:** The `slice()` method creates a shallow copy of a portion of an array. Using `slice(-1)[0]`, we take a slice starting from the last element and retrieve the first (and only) element in that slice.
   - **Code:** `var c = arr.slice(-1)[0]`

* **Pros:** Can be useful for situations where you need to work with a subarray containing the last element, not just access it directly.  It's also more explicit about creating a copy of the data.
* **Cons:** Slightly more verbose than `length` or `at()`, and can potentially have a minor performance overhead due to creating a new array.

**Other Considerations:**

* **Array Size:** For very large arrays, the difference in performance between these methods might become more significant.  
* **Task:** If you only need the last element, `at()` is generally recommended for its simplicity and performance.

Let me know if you'd like to explore any of these aspects further!

Related benchmarks:

Get last element of array2 (version: 0)

Comparing performance of: length vs at vs slice

Created: 3 years ago by: Guest

Jump to the latest result

length

at

slice

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model gemma2:9b, generated one year ago):