Benchmark: Test for / for each

Script Preparation code:

var a = [];
for (let i=0; i<100000; i++)
  a.push(i);

Tests:

For
let sum = 0; for (let i = 0; i < a.length; i++) sum += a[i];
For Each
let sum = 0; a.forEach(i => sum += i);

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
For
For Each

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 3 years ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/90.0.4430.212 Safari/537.36

Browser/OS: Chrome 90 on Windows

View result in a separate tab

Test name	Executions per second
For	66.7 Ops/sec
For Each	699.6 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's break down the provided benchmark and explain what's being tested, compared options, pros/cons, and other considerations.

**Benchmark Definition:**
The benchmark is designed to compare the performance of two JavaScript loops: `for` and `for each`.

**Script Preparation Code:**
The script preparation code creates an array `a` with 100,000 elements, populated with numbers from 0 to 99,999. This array will be used as input for both tests.

**Html Preparation Code:**
There is no HTML preparation code provided, which means the benchmark only runs in a Node.js environment or a similar context where HTML is not relevant.

**Individual Test Cases:**

1. **For**: This test case uses a traditional `for` loop to iterate over the array `a`. The loop variable `i` is initialized to 0 and incremented by 1 in each iteration, until it reaches the length of the array (100,000). The value of `i` is added to the sum variable.
2. **For Each**: This test case uses the `forEach()` method, which iterates over the elements of the array `a`. In this implementation, the callback function takes a single argument `i`, which represents each element of the array. The sum variable is updated by adding `i` to it.

**Comparison:**
The benchmark compares the performance of these two loop types:

* **For**: This traditional loop uses a counter variable and manual incrementation.
* **For Each**: This loop type uses an iterator (the callback function) and does not require manual incrementation.

**Pros/Cons:**

* **For**:
	+ Pros: More control over the iteration process, potentially better performance for specific use cases.
	+ Cons: Requires manual incrementation of the counter variable, which can be error-prone.
* **For Each**:
	+ Pros: Convenient and concise way to iterate over arrays, eliminates the need for manual incrementation.
	+ Cons: May have overhead due to function call and iterator management.

**Library:**
In this benchmark, no external libraries are used. The `forEach()` method is a built-in JavaScript method.

**Special JS Feature/Syntax:**
The benchmark uses the arrow function syntax (`i => sum += i`) in the `for each` test case. This syntax allows for concise and readable code without defining an explicit function.

**Other Considerations:**

* **Cache locality**: In the `for` loop, accessing elements of the array sequentially (e.g., `a[i]`, `a[i+1]`) can improve cache locality, as modern CPUs optimize performance by minimizing cache misses. The `forEach()` method, on the other hand, may access elements in a more random order, which could negatively impact cache locality.
* **Overhead**: The `for each` loop may incur additional overhead due to function call and iterator management.

**Alternatives:**
Other loop types that can be used instead of `for` or `forEach()` include:

* **While Loop**: A traditional while loop that iterates until a condition is met.
* **Reduce() Method**: A built-in JavaScript method for reducing arrays to a single value by applying a callback function to each element.

These alternatives may offer different performance profiles, depending on the specific use case and requirements.

Related benchmarks:

Test for / for each (version: 0)

Comparing performance of: For vs For Each

Created: 3 years ago by: Guest

Jump to the latest result

For

For Each

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

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