Benchmark: Array.at(-1) vs. Array.length - 1

Script Preparation code:

var LEN = 3000;
var arr = new Array(LEN).fill(0).map((_, i) => i);

Tests:

.at(-1)
var other = arr.at(-1);
length - 1
var other = arr[arr.length - 1]
const LEN - 1
var other = arr[LEN - 1]

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
.at(-1)
length - 1
const LEN - 1

Fastest: N/A

Slowest: N/A

Latest run results:

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

User agent: Mozilla/5.0 (X11; Linux x86_64; rv:122.0) Gecko/20100101 Firefox/122.0

Browser/OS: Firefox 122 on Linux

View result in a separate tab

Test name	Executions per second
.at(-1)	403976320.0 Ops/sec
length - 1	583154816.0 Ops/sec
const LEN - 1	595068736.0 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's break down the provided JSON and benchmark code to understand what's being tested.

**Benchmark Definition**

The benchmark definition is a single line of JavaScript that compares the performance of three different approaches:

* `Array.at(-1)`
* `arr.length - 1`
* `const LEN - 1`

In this case, we're using a variable `LEN` initialized with 3000 to create an array with that many elements. Each element is assigned a value of its index `i` using the `map()` method.

**Library Usage**

There's no explicit library mentioned in the benchmark definition or test cases. However, it's likely that some libraries might be used indirectly through browser-specific features or built-in methods.

**JavaScript Features/Syntax**

The benchmark uses the following JavaScript feature:

* The spread operator (`=>`) is used to define an anonymous function (a lambda expression) within the `map()` method.
* The `const` keyword is used to declare a variable `LEN` with a value that will be evaluated at compile-time.

**Options Compared**

The three options being compared are:

1. **`.at(-1)`**: This is a modern JavaScript feature introduced in ECMAScript 2019, which allows accessing the last element of an array by its index.
2. **`arr.length - 1`**: This approach uses the `length` property to access the length of the array and then subtracts 1 from it to get the index of the last element.
3. **`const LEN - 1`**: This option is a bit more explicit, as it calculates the index by subtracting 1 from the predefined constant `LEN`.

**Pros and Cons**

Here's a brief summary of each approach:

* `.at(-1)`:
	+ Pros: concise and expressive, modern JavaScript feature.
	+ Cons: might not be supported in older browsers or environments.
* `arr.length - 1`:
	+ Pros: widely supported, easy to read and understand.
	+ Cons: requires two separate operations (getting the length and subtracting 1).
* `const LEN - 1`:
	+ Pros: explicit and controlled, uses a constant value.
	+ Cons: less concise than `.at(-1)` or `arr.length - 1`, might be seen as more verbose.

**Other Alternatives**

Some alternative approaches that are not being tested in this benchmark include:

* Using `arr[arr.length - 2]` to access the second-to-last element (which would require two operations: getting the length and subtracting 1).
* Using a traditional loop or recursion to iterate over the array elements.
* Using other array methods, such as `find()` or `reduce()`, which might have different performance characteristics.

Keep in mind that this benchmark is focused on comparing the performance of these three specific approaches.

Related benchmarks:

Array.at(-1) vs. Array.length - 1 (version: 0)

Comparing performance of: .at(-1) vs length - 1 vs const LEN - 1

Created: one year ago by: Guest

Jump to the latest result

.at(-1)

length - 1

const LEN - 1

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):