Benchmark: Getting last element of array (no cash arr.length)

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

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	74242.5 Ops/sec
length	2753223.0 Ops/sec

Autogenerated LLM Summary (model gpt-4o-mini, generated 9 months ago):

LLMs can make mistakes. Check important info.

The benchmark represented in the provided JSON tests the performance of two different methods for accessing the last element of a large array in JavaScript. The two methods being compared are:

1. **Using `Array.prototype.slice()`** (denoted by the test name "slice"):
   - Benchmark Definition: 
     ```javascript
     for (let i = 0; i < 1000; i++) {
       const v = arr.slice(-1)[0];
     }
     ```
   - Here, the last element of the array is obtained using the `slice` method, which creates a shallow copy of the array but only contains the last element (due to the `-1` index).

2. **Using direct indexing with `arr.length`** (denoted by the test name "length"):
   - Benchmark Definition: 
     ```javascript
     for (let i = 0; i < 1000; i++) {
       const v = arr[arr.length - 1];
     }
     ```
   - This method accesses the last element directly using the `length` property of the array, which is typically faster because it does not create a new array.

### Pros and Cons
- **Using `slice`:**
  - **Pros:** 
    - The syntax can be cleaner in certain contexts, especially when extracting multiple elements or performing manipulations on subarrays.
  - **Cons:** 
    - It involves creating a new array, which incurs additional overhead in both time and memory, especially for large arrays.
  
- **Using `length`:**
  - **Pros:** 
    - This approach is generally more efficient because it directly accesses the last element without creating any copies. It is also very readable and straightforward.
  - **Cons:** 
    - There are fewer complexities with indexing, but for simple retrieval, this method is preferable over `slice`.

### Performance Results
From the benchmark results, we can see a measurable difference between the two methods when executed:

- The "length" method achieved approximately **2,753,223 executions per second**.
- The "slice" method achieved approximately **74,242 executions per second**.

This significant performance difference indicates that the direct indexing method using `arr.length` is far more efficient for accessing the last element.

### Other Considerations
- While `slice` is a valid method and may be used for clarity or other extraction needs, in performance-critical applications where access speed is paramount, the direct indexing method is recommended.
- For large arrays, the memory implications of creating new arrays with `slice` also need to be considered, as excessive use can lead to increased garbage collection overhead.
- Alternatives for maintaining optimal performance include avoiding unnecessary array duplication and considering the overall design and access patterns when working with large datasets.

### Alternative Approaches
- Other alternative approaches could involve:
  - Utility libraries or frameworks that provide optimized functions for array manipulations, albeit usually resulting in extra overhead.
  - Implementing custom functions tailored for specific use cases in environments where array access is frequent.

Overall, this benchmark provides clear insights into the efficiency of different methods for accessing array elements in JavaScript, emphasizing the importance of choosing the right approach for performance-critical applications.

Related benchmarks:

Getting last element of array (no cash arr.length) (version: 1)

Comparing performance of: slice vs length

Created: 9 months 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 gpt-4o-mini, generated 9 months ago):