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

Script Preparation code:

var array = [];

for(var i = 0; i < 100000; i++){array.push(Math.random());}

Tests:

length - 1
array[array.length - 1];
at(-1)
array.at(-1);

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
length - 1
at(-1)

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: one year ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/133.0.0.0 Safari/537.36

Browser/OS: Chrome 133 on Windows

View result in a separate tab

Test name	Executions per second
length - 1	98919184.0 Ops/sec
at(-1)	95449264.0 Ops/sec

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

LLMs can make mistakes. Check important info.

I'd be happy to explain the benchmark and its options.

**Benchmark Overview**

The provided JSON represents a JavaScript microbenchmark test case, specifically measuring the performance difference between accessing array elements using two different methods: `at(-1)` and `length - 1`.

**Script Preparation Code**

The script preparation code creates an empty array with 100,000 random elements. This is done to ensure that both benchmarking methods access the entire array.

```javascript
var array = [];
for (var i = 0; i < 100000; i++) {
    array.push(Math.random());
}
```

**Benchmark Definition**

The benchmark definition specifies two test cases:

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

These methods both access the last element of the array.

**Library and Syntax**

Neither of these methods uses a library, and there are no special JavaScript features or syntax used in this benchmark.

**Options Compared**

The two options compared are:

* `length - 1`: This method accesses the last element by subtracting 1 from the length of the array. It is a simple and straightforward way to access an element at a specific index.
* `at(-1)`: This method accesses the last element using the `at()` method, which was introduced in ECMAScript 2019 (ES10). The `at()` method allows you to specify the index of an array using the dot notation (`array.at(index)`).

**Pros and Cons**

Here are some pros and cons of each approach:

* `length - 1`:
	+ Pros: Widely supported, no dependency on modern browsers.
	+ Cons: May not be as efficient or readable, especially for large arrays.
* `at(-1)`: (Note: The `-1` indexing in the benchmark definition is a bit confusing. In modern JavaScript, you would typically use `array.at(-1)` without quotes.)
	+ Pros: More readable and efficient than `length - 1`, especially for larger arrays.
	+ Cons: Requires support for modern browsers and ECMAScript 2019 features.

**Other Considerations**

When choosing between these two methods, consider the following:

* If you need to access elements at a specific index in an older browser or environment, `length - 1` might be a better choice.
* If you're writing new code for modern browsers and want to take advantage of efficient indexing, `at(-1)` is likely the better option.

**Alternatives**

Other alternatives for accessing array elements include:

* Using `slice()` with negative offset (e.g., `array.slice(array.length - 1)`)
* Using `index` property on the `Array.prototype` object (not recommended)
* Using a simple loop to iterate over the array and access the desired element

Related benchmarks:

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

Comparing performance of: length - 1 vs at(-1)

Created: 3 years ago by: Guest

Jump to the latest result

length - 1

at(-1)

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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