Benchmark: reversed versus ordered (+ cached)

Script Preparation code:

var array = [];
for (let i = 0 ; i < 10000 ; i++) {
	array.push (Math.random () * 100);
}

Tests:

ordered
let sum = 0; for (let i = 0 ; i < array.length ; i++) sum += array[i];
reversed
let sum = 0; for (let i = array.length - 1 ; i >= 0 ; i--) sum += array[i];
ordered cached
let sum = 0; let length = array.length; for (let i = 0 ; i < length ; i++) sum += array[i];

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
ordered
reversed
ordered cached

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model gpt-4o-mini, generated 13 days ago):

LLMs can make mistakes. Check important info.

The benchmark defined in the provided JSON tests the performance of summing up the elements of an array using different loop approaches in JavaScript. Here's a breakdown of the various test cases, their implications, and considerations.

### Test Cases

1. **Ordered Loop:**
   ```javascript
   let sum = 0;
   for (let i = 0; i < array.length; i++)
       sum += array[i];
   ```
   - **Description:** This test sums the elements of the array in the order they are stored, iterating from the first element to the last.
   - **Pros:** 
     - This approach is straightforward and readable.
     - It takes advantage of direct access to each array element.
   - **Cons:** 
     - It does not cache the length of the array, which may lead to performance overhead in some JavaScript engines when the length is evaluated on each iteration.

2. **Reversed Loop:**
   ```javascript
   let sum = 0;
   for (let i = array.length - 1; i >= 0; i--)
       sum += array[i];
   ```
   - **Description:** This version iterates through the array backward, starting from the last element and moving to the first.
   - **Pros:** 
     - Sometimes, iterating backward can be beneficial in specific scenarios, especially if you're performing operations that may alter the array during iteration (not the case here).
   - **Cons:** 
     - Generally, there are no significant performance advantages to iterating backward in this case, and readability may suffer for developers who expect forward iteration.

3. **Ordered Cached Loop:**
   ```javascript
   let sum = 0;
   let length = array.length;
   for (let i = 0; i < length; i++)
       sum += array[i];
   ```
   - **Description:** This approach caches the length of the array in a variable (`length`) before entering the loop, thereby avoiding repeated access to `array.length` during each iteration.
   - **Pros:**
     - Caching the array length can enhance performance, especially if the array is large, since it eliminates the need to repeatedly read the length property.
   - **Cons:**
     - It adds a minor variable assignment, but this overhead is generally negligible compared to the potential performance gains, especially for larger datasets.

### Performance Results

The execution results from the benchmark indicate that:

- The **ordered cached** loop performed the best, with **1634.21 executions per second**.
- The **reversed** loop closely followed at **1630.22 executions per second**.
- The **ordered** loop had the lowest performance, clocking in at **807.71 executions per second**, apparently due to the repeated access of `array.length` in each loop iteration.

### Other Considerations

**Language Feature:**  
The benchmark makes use of the `let` keyword introduced in ES6 (ECMAScript 2015). This allows block scoping for the loop variable (`i`), which is a more modern syntax compared to the oldest ways of declaring variables using `var`. This is advantageous as it prevents variable hoisting issues and reduces the risk of creating unintended global variables.

**Alternatives:**  
Other alternatives for summing an array include:

- **Using `Array.prototype.reduce()`:**
  ```javascript
  const sum = array.reduce((acc, curr) => acc + curr, 0);
  ```
  - This approach is functional, elegant, and concise but could be less performant than loops due to function call overhead.
  
- **Using a `for...of` loop:**
  ```javascript
  let sum = 0;
  for (const value of array) {
      sum += value;
  }
  ```
  - This modern syntax is readable and avoids the need for index manipulation.

- **Using `Array.prototype.forEach()`:**
  ```javascript
  let sum = 0;
  array.forEach(value => {
      sum += value;
  });
  ```
  - Similar to `.reduce()`, it is clean but may have performance considerations due to the callback function's overhead.

### Conclusion

The benchmark effectively tests different looping constructs to evaluate their performance in summing values in an array. The choice between these approaches can vary based on the context of use, array size, and performance requirements, demonstrating the importance of understanding both the language capabilities and their impacts on performance.

Latest run results:

Run details: (Test run date: 13 days ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/130.0.0.0 Safari/537.36

Browser/OS: Chrome 130 on Windows

View result in a separate tab

Test name	Executions per second
ordered	807.7 Ops/sec
reversed	1630.2 Ops/sec
ordered cached	1634.2 Ops/sec

Related benchmarks:

reversed versus ordered (+ cached) (version: 1)

Comparing performance of: ordered vs reversed vs ordered cached

Created: 13 days ago by: Guest

Jump to the latest result

ordered

reversed

ordered cached

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model gpt-4o-mini, generated 13 days ago):