Benchmark: Test slice vs array.length accessing last element

Script Preparation code:

var arr = Array.from(Array(100).keys());

Tests:

Using slice
var last = arr.slice(-1)[0]
Using length
var last = arr[arr.length-1]

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Using slice
Using length

Fastest: N/A

Slowest: N/A

Latest run results:

No previous run results

This benchmark does not have any results yet. Be the first one to run it!

Autogenerated LLM Summary (model llama3.1:latest, generated one year ago):

LLMs can make mistakes. Check important info.

Let's dive into the benchmarking results.

**What is being tested?**

The provided JSON represents a benchmark test case that compares two different approaches to accessing the last element of an array:

1. Using `slice(-1)[0]`
2. Using `arr.length-1` and indexing into the array directly

**What options are compared?**

Two JavaScript methods are being compared:

### Method 1: Using `slice(-1)[0]`

This approach uses the `slice()` method to create a shallow copy of the last element from the original array. The `-1` argument tells `slice()` to start at the end of the array and return one element.

Example code:
```javascript
var arr = Array.from(Array(100).keys());
var last = arr.slice(-1)[0];
```
### Method 2: Using `arr.length-1`

This approach directly accesses the length property of the array and subtracts 1 to get the index of the last element. Then, it uses that index to access the corresponding value in the array.

Example code:
```javascript
var arr = Array.from(Array(100).keys());
var last = arr[arr.length-1];
```
**Pros/Cons of each approach:**

### Method 1 (slice(-1)[0])

Pros:

* Simple and concise syntax
* No need to explicitly calculate the length of the array

Cons:

* Creates an additional shallow copy of the array, which might incur some overhead for large arrays

### Method 2 (arr.length-1)

Pros:

* Directly accesses the last element without creating a new array copy

Cons:

* Requires explicit calculation of the length property and subtraction to get the index

**Other considerations:**

Both methods are generally efficient, but the difference in performance lies in the overhead of creating an additional array copy using `slice()`. The results suggest that directly accessing the last element using `arr.length-1` is faster than using `slice()`.

**Library or special JS feature usage:**

None in this benchmark.

**Other alternatives:**

* Using `pop()` method to remove and return the last element of an array. This approach is not shown in the provided test case but is another valid way to access the last element.
```javascript
var arr = Array.from(Array(100).keys());
var last = arr.pop();
```
This method has its own pros and cons, such as modifying the original array (if you don't want to remove the last element) or requiring additional handling for edge cases.

Keep in mind that this benchmark is focused on a specific scenario (accessing the last element of an array), so these alternatives might not be directly comparable.

Related benchmarks:

Test slice vs array.length accessing last element (version: 0)

Comparing performance of: Using slice vs Using length

Created: 3 years ago by: Guest

Jump to the latest result

Using slice

Using length

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

No previous run results

Autogenerated LLM Summary (model llama3.1:latest, generated one year ago):