Benchmark: Getting last element of array

Script Preparation code:

var arr = [];
for (let i = 0; i < 1000000; i++) {
    arr.push(i);
}

Tests:

slice
for (let i = 0; i < 1000; i++) { const v = arr.slice(-1)[0]; }
length
let len = arr.length - 1 for (let i = 0; i < 1000; i++) { const v = arr[len]; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
slice
length

Fastest: N/A

Slowest: N/A

Latest run results:

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

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/18.3 Safari/605.1.15

Browser/OS: Safari 18 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
slice	77439.2 Ops/sec
length	2954541.2 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's break down the provided JSON and explain what's being tested, compared options, pros and cons, and other considerations.

**Benchmark Definition**
The benchmark is testing two approaches to get the last element of an array: using `slice()` method or accessing the array length directly (`length` property).

**Script Preparation Code**
The script preparation code creates a large array with 1 million elements and assigns it to the variable `arr`. This ensures that both test cases operate on a large enough dataset.

**Html Preparation Code**
There is no HTML preparation code provided, which means that only the JavaScript aspect of the benchmark is being tested.

**Options Compared**

1. **Using slice() method**: The first test case uses the `slice()` method to get the last element of the array. Specifically, it calls `arr.slice(-1)[0]`.
2. **Accessing length directly**: The second test case accesses the array length directly using `len = arr.length - 1` and then uses this value to get the last element.

**Pros and Cons**

* **Using slice() method**:
	+ Pros: Generally considered more reliable and efficient, as it handles cases where the array is modified.
	+ Cons: May be slower for very large arrays due to its overhead.
* **Accessing length directly**:
	+ Pros: Can be faster for very large arrays, as it doesn't involve creating a new slice object.
	+ Cons: May not handle cases where the array is modified.

**Other Considerations**

* The benchmark uses a relatively small dataset (1 million elements) to test both approaches. For very large datasets, the performance difference between these two methods might be negligible.
* It's worth noting that in modern JavaScript engines, the `slice()` method has become more efficient due to optimizations like tail call optimization.

**Library Used**

None mentioned explicitly in the provided JSON. However, if we assume that the benchmark is using a standard JavaScript implementation (e.g., V8), then no additional libraries are required.

**Special JS Feature/Syntax**
There doesn't seem to be any special JavaScript features or syntax used in this benchmark.

**Alternatives**

Other approaches to get the last element of an array include:

1. `arr[arr.length - 1]`: Similar to accessing length directly, but using the property access syntax.
2. `Math.max.apply(null, arr)`: Using the `max` function and applying it to the array with `null` as the initial value.
3. `Array.prototype.at()`: A newer ES6 method (available in modern browsers and Node.js) that returns the element at a given index.

These alternatives might offer different performance characteristics or trade-offs, but they are not explicitly tested in this benchmark.

The provided benchmark is a simple yet informative test case for comparing the performance of two common approaches to get the last element of an array.

Related benchmarks:

Getting last element of array (version: 0)

Comparing performance of: slice vs length

Created: 2 years ago by: Guest

Jump to the latest result

slice

length

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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