Benchmark: array[array.length - 1] vs array.at(-1) vs array[len -1]

Script Preparation code:

var array = [1,2,3];

Tests:

array[array.length - 1]
const d = array[array.length - 1];
array.at(-1)
const z = array.at(-1);
array[len - 1]
const len = array.length; const a = array[len - 1];

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
array[array.length - 1]
array.at(-1)
array[len - 1]

Fastest: N/A

Slowest: N/A

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/129.0.0.0 Safari/537.36

Browser/OS: Chrome 129 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
array[array.length - 1]	14538164.0 Ops/sec
array.at(-1)	26884256.0 Ops/sec
array[len - 1]	14491580.0 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's dive into the world of JavaScript microbenchmarks on MeasureThat.net.

**Benchmark Definition**

The provided JSON represents a benchmark test that compares three different ways to access the last element in an array:

1. `array[array.length - 1]`
2. `array.at(-1)`
3. `array[len - 1]`

These methods aim to achieve the same result, but they use distinct syntax and may have varying performance characteristics.

**Options Compared**

The benchmark tests three different options for accessing the last element in an array:

* `array[array.length - 1]`: This method uses direct indexing with a numeric value. It's a straightforward way to access an array element by its index.
* `array.at(-1)`: Introduced in ECMAScript 2019, this method provides a more modern and flexible way to access array elements using dot notation (e.g., `array.at(-1)`). It throws a `RangeError` if the index is out of range.
* `array[len - 1]`: This method uses direct indexing with a string value representing the length of the array. While it's equivalent to `array[array.length - 1]`, it's less readable and more prone to errors.

**Pros and Cons**

Here are some pros and cons for each approach:

* `array[array.length - 1]`:
	+ Pros: Simple, well-established syntax.
	+ Cons: Can lead to off-by-one errors if not used carefully.
* `array.at(-1)`:
	+ Pros: More readable and intuitive than direct indexing with numbers or strings.
	+ Cons: May introduce unnecessary overhead due to the check for out-of-range indices.
* `array[len - 1]`:
	+ Pros: None notable.
	+ Cons: Less readable, more prone to errors, and generally discouraged in favor of `at(-1)`.

**Library Usage**

None of the provided benchmark tests explicitly use any external libraries. The syntax and behavior are standard JavaScript.

**Special JS Features or Syntax**

The `array.at(-1)` method is a relatively recent addition to the ECMAScript specification (2019). It's part of the " Array.prototype.at()" standardization effort, which aims to provide a more modern way to access array elements using dot notation.

**Other Considerations**

When choosing an approach for accessing the last element in an array, consider factors such as:

* Readability and maintainability
* Performance (avoid unnecessary overhead)
* Error handling (handle out-of-range indices carefully)
* Compatibility with different JavaScript versions and environments

As for alternatives, other methods for accessing array elements include:

* `array[-1]`: This method is equivalent to `array.at(-1)` but uses square brackets instead of dot notation. It's less readable and discouraged in favor of the more modern `at()` syntax.
* `new Array(array.length - 1).indexOf(array[array.length - 1])`: This approach involves creating a new array with the same length as the original, then finding its index using `indexOf()`. While it works, it's inefficient and not recommended.

I hope this explanation helps software engineers understand the JavaScript microbenchmark on MeasureThat.net!

Related benchmarks:

array[array.length - 1] vs array.at(-1) vs array[len -1] (version: 0)

Comparing performance of: array[array.length - 1] vs array.at(-1) vs array[len - 1]

Created: one year ago by: Guest

Jump to the latest result

array[array.length - 1]

array.at(-1)

array[len - 1]

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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