Benchmark: Array: get last item

Script Preparation code:

var arr = Array.from({length: 1000}, (_,i) => i + 1)

Tests:

length
console.log(arr[arr.length-1])
slice
console.log(arr.slice(-1))

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
length
slice

Fastest: N/A

Slowest: N/A

Latest run results:

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

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Let's break down the benchmark and its test cases.

**Benchmark Definition JSON**

The provided JSON represents a JavaScript microbenchmark named "Array: get last item". The `Script Preparation Code` section generates an array of 1000 elements, starting from 1. This array will be used to test two different approaches for accessing the last element.

**Test Cases**

There are two test cases:

1. **"length"**: This test case uses the built-in property `arr.length` to access the last element of the array.
2. **"slice"**: This test case uses the `Array.prototype.slice()` method with a negative argument `-1` to access the last element of the array.

**Options Compared**

The two test cases are comparing the performance of accessing the last element of an array using:

* The built-in property `arr.length`
* The `Array.prototype.slice()` method with a negative argument `-1`

**Pros and Cons**

* **"length"**: This approach is very simple and straightforward. It has a low overhead since it only accesses a property on the array object.
	+ Pros: Simple, fast, and low overhead
	+ Cons: May be slower than other approaches that access elements by index
* **"slice"**: This approach uses the `Array.prototype.slice()` method to create a new array with the last element. While it may seem like an extra operation, modern JavaScript engines are optimized for this method, making it relatively fast.
	+ Pros: May be faster than accessing `arr.length` due to optimizations in the engine
	+ Cons: Requires creating a new array, which can have overhead

**Other Considerations**

* **Array.prototype.slice()**: The `slice()` method returns a new array object containing the elements of the original array from start index (0) up to but not including the end index. By passing `-1` as the end index, we effectively get the last element of the array.
* **JavaScript Engines**: Modern JavaScript engines are optimized for performance and often have built-in support for common array operations like `slice()`. This means that the actual performance difference between these two approaches may be negligible.

**Alternatives**

Other alternatives to accessing the last element of an array include:

* Using `arr[arr.length-1]` (a simple increment of the index)
* Using a loop or recursion to iterate over the elements and find the last one
* Using other methods like `Array.prototype.find()` or `Array.prototype.lastIndexOf()`

However, these alternatives may have different performance characteristics and overhead, depending on the specific implementation and JavaScript engine.

In summary, the "length" approach is simple and low-overhead, while the "slice" approach may be faster due to optimizations in modern JavaScript engines. The choice of approach depends on the specific requirements and trade-offs desired.

Related benchmarks:

Array: get last item (version: 0)

Comparing performance of: length vs slice

Created: 4 years ago by: Guest

Jump to the latest result

length

slice

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

No previous run results

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