Benchmark: for loop vs for-of with index variable2

Script Preparation code:

   var arr1 = [];
   var arr2 = [];
   for (var i = 0; i < 10000; i++) {
       arr1[i] = i;
       arr2[i] = i;
   }

Tests:

for
var arr = []; for (var i = 0; i < arr2.length; i++) { arr.push({ a: arr1[i], b: arr2[i] }); }
for of with index
var arr = []; var index = 0; for (var val of arr2) { arr.push({ a: arr1[index++], b: arr2 }); }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
for
for of with index

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 llama3.2:3b, generated one year ago):

LLMs can make mistakes. Check important info.

I'll break down the provided JSON and explain what's being tested, the pros and cons of each approach, and other considerations.

**Benchmark Definition**

The benchmark is comparing two approaches to iterate over an array:

1. **Traditional for loop**: The script prepares two arrays, `arr1` and `arr2`, with 10,000 elements. It then iterates using a traditional for loop to populate another array, `arr`.
2. **For-of loop with index variable**: Similar to the traditional for loop, but instead of using an incrementing counter, it uses a for-of loop with an index variable (`var index`) to access the elements of `arr2` and assign them to `arr`.

**Library**

There is no explicit library mentioned in the benchmark definition. However, both examples use the Array prototype's methods (`length`, `push()`, and indexing) which are built-in JavaScript features.

**Special JS Feature or Syntax**

None explicitly mentioned, but it's worth noting that for-of loops were introduced in ECMAScript 2015 (ES6), so this benchmark is testing a relatively new feature. However, the code uses a legacy syntax (`var i = 0;` instead of `let i = 0;` or `const i = 0;`) which may not be optimal from a modern JavaScript perspective.

**Pros and Cons**

1. **Traditional for loop**:
	* Pros: Widely supported, easy to read, and maintain.
	* Cons: Can lead to off-by-one errors, slower performance due to unnecessary array indexing checks.
2. **For-of loop with index variable**:
	* Pros: More concise, eliminates the need for manual indexing, and can be faster (due to reduced branching).
	* Cons: May not be as readable for beginners or less experienced developers, as it requires understanding of the iterator protocol.

**Considerations**

* Both approaches have similar execution counts, but the for-of loop with index variable has a slightly higher executions per second rate.
* The benchmark is using Firefox 81 and a Mac OS X 10.14 environment. Results may vary across different browsers, platforms, and versions.
* The script preparation code is relatively simple, which might be an optimal scenario for this specific test.

**Other Alternatives**

If you wanted to test alternative approaches, some possibilities could include:

1. **Using `forEach()`**: Instead of a traditional for loop or for-of loop with index variable, using the `forEach()` method on an array.
2. **Using `map()`**: Similar to `forEach()`, but using `map()` to create a new array instead.
3. **Using `reduce()`**: Instead of creating a new array using `push()`, using `reduce()` to accumulate values in a single result.

These alternatives would require modifications to the benchmark definition and script preparation code, and would be worth exploring if you're looking for more variation in the testing scenarios.

Related benchmarks:

for loop vs for-of with index variable2 (version: 0)

Comparing performance of: for vs for of with index

Created: 5 years ago by: Guest

Jump to the latest result

for

for of with index

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):