Benchmark: for vs for reverse

Script Preparation code:

a=['a','b','c'];for(let i=0; i<15; i++) a.push(...a)

Tests:

reverse
for(let i=a.length-1; i>=0; i--) b=i;
normal
for(let i=0; i<a.length; i++) b=i;

Historical Performance Data aggregated from 5 community runs

Desktop Results:

Chrome 5 runs

reverse

210/s

normal

116/s

Fastest: reverse (1.8x faster)

View exact numbers

✓ reverse: 210 ops/sec
• normal: 116 ops/sec

Results show median performance across all community submissions. Run this benchmark yourself to verify on your device.

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
reverse
normal

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 2 years ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36

Browser/OS: Chrome 120 on Windows

View result in a separate tab

reverse

211/s

normal

116/s

View exact numbers

Test name	Executions per second
✓ reverse	211 Ops/sec
normal	116 Ops/sec

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

LLMs can make mistakes. Check important info.

I'd be happy to explain the benchmark and its options.

**Benchmark Overview**

The benchmark compares two approaches for iterating over an array in reverse order: using a traditional `for` loop with a decrementing counter (`normal`) versus using a `for...of` loop with a reversed iterator (`reverse`). The goal is to determine which approach is faster.

**Options Compared**

There are only two options being compared:

1. **Traditional `for` loop with decrementing counter**: This approach uses a traditional `for` loop with a counter that decrements on each iteration. The counter starts at the length of the array minus one and goes down to zero.
2. **`for...of` loop with reversed iterator**: This approach uses a `for...of` loop with an iterator that yields values in reverse order.

**Pros and Cons**

* **Traditional `for` loop:**
	+ Pros:
		- Well-established and widely supported syntax
		- Easy to understand and implement for those familiar with traditional loops
	+ Cons:
		- May have overhead due to the need to manage a counter variable
		- Can be less efficient than other approaches, especially for large arrays
* **`for...of` loop with reversed iterator:**
	+ Pros:
		- More concise and expressive syntax
		- Can be more efficient, as the loop is optimized by the engine
	+ Cons:
		- May not be as well-established or widely supported as traditional `for` loops
		- Requires understanding of iterators and the syntax

**Library Usage**

There are no external libraries used in this benchmark. The only library mentioned is not actually required for this specific test.

**Special JS Feature/Syntax**

The benchmark uses a special JavaScript feature: **iterators**. Specifically, it uses a reversed iterator to iterate over an array in reverse order. This feature is supported by most modern browsers and engines.

**Other Considerations**

* **Array size**: The benchmark iterates over arrays of length 15. Larger arrays may exhibit different performance characteristics due to the increasing overhead of JavaScript operations.
* **Browser engine**: The benchmark runs on a specific browser engine (Chrome) with a particular version (120). Different browsers and engines may have varying levels of optimization for this type of loop.

**Alternative Approaches**

Other approaches that could be used to iterate over an array in reverse order include:

* Using `Array.prototype.reverse()`: This method reverses the entire array in place, but has a time complexity of O(n).
* Using a recursive function: A recursive function can be used to iterate over an array in reverse order, but may have performance implications due to the overhead of repeated function calls.
* Using a library like Lodash or Underscore.js: These libraries provide a `reverse()` function for arrays, which can simplify the implementation.

However, these alternative approaches are not specifically addressed by this benchmark.

for vs for reverse (version: 0) Benchmark.js

for vs for reverse

Comparing performance of: `reverse vs normal`

Created: 2 years ago by: Guest

Go to the latest result

reverse

normal

Historical Performance Data aggregated from 5 community runs

Desktop Results:

Chrome 5 runs

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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

for vs for reverse (version: 0) Benchmark.js

for vs for reverse

Comparing performance of: reverse vs normal

Created: 2 years ago by: Guest

Go to the latest result

reverse

normal

Historical Performance Data aggregated from 5 community runs

Desktop Results:

Chrome 5 runs

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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

Comparing performance of: `reverse vs normal`