Benchmark: for vs for (reverse with length) vs every vs forEach with big array 2

Script Preparation code:

function generateTestArray() {
	var result = [];

	for (let i = 0; i < 1000000; ++i) {
		result.push({
			a: i,
			b: i / 2,
			r: 0,
		});
	}

	return result;
}

var array = generateTestArray();

Tests:

for
for (var i = 0; i < array.length; i++) { array[i]; }
for (reverse with length)
var length = array.length; for (var i = length; --i >= 0;) { array[i]; }
some
array.some(function(i) { array[i]; return false; });
every
array.every(function(i) { array[i]; return true; });
forEach
array.forEach(function(i) { array[i]; });

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
for
for (reverse with length)
some
every
forEach

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/103.0.5060.134 Safari/537.36 Edg/103.0.1264.77

Browser/OS: Chrome 103 on Windows

View result in a separate tab

Test name	Executions per second
for	5.7 Ops/sec
for (reverse with length)	9.9 Ops/sec
some	5.0 Ops/sec
every	4.9 Ops/sec
forEach	4.7 Ops/sec

Autogenerated LLM Summary (model llama3.2:3b, generated 5 months ago):

LLMs can make mistakes. Check important info.

Let's break down the provided benchmark and its test cases.

**Benchmark Overview**

The benchmark is designed to compare the performance of four different loop constructs in JavaScript: `for`, `for (reverse with length)`, `every`, and `forEach`. The test array is generated using a custom function that creates an array of 1 million objects with specific properties. The benchmarks are run on a desktop browser instance.

**Loop Constructs**

Here's a brief explanation of each loop construct:

*   **`for`**: A traditional `for` loop that iterates over the indices of the array.
*   **`for (reverse with length)`**: This is a variation of the traditional `for` loop that uses the array's `length` property as the counter and decrements it in each iteration, effectively iterating from the last index to the first.
*   **`some`**: A method that returns `true` if at least one element in the array passes a test function. It iterates over the elements until it finds one that meets the condition or reaches the end of the array.
*   **`every`**: A method that returns `true` if all elements in the array pass a test function. It iterates over the elements and stops as soon as it finds an element that doesn't meet the condition.
*   **`forEach`**: A method that executes a provided callback function for each element in the array, without returning any value.

**Performance Comparison**

The benchmark measures the performance of each loop construct by executing them multiple times (9.945130348205566 executions per second for "for" with length) and reporting the average execution time. The results are as follows:

*   **`for`**: 5.721550941467285 executions per second
*   **`for (reverse with length)`**: 4.959159851074219 executions per second
*   **`some`**: 4.928965091705322 executions per second
*   **`every`**: 4.733727931976318 executions per second
*   **`forEach`**: 4.733727931976318 executions per second

**Pros and Cons**

Here's a summary of the pros and cons for each loop construct:

*   **`for`**: Pros: simple, easy to read; Cons: can be slow due to array indexing.
*   **`for (reverse with length)`**: Pros: efficient use of `length` property; Cons: less readable than traditional `for`.
*   **`some`**: Pros: stops iterating as soon as condition is met; Cons: may not be suitable for arrays with many false positives.
*   **`every`**: Pros: easy to read and understand; Cons: can be slow due to array indexing.
*   **`forEach`**: Pros: concise and readable; Cons: may not be suitable for loops that require more control over iteration.

**Library/External Functionality**

There is no external library or functionality used in this benchmark. The custom function `generateTestArray()` generates the test array, and the loop constructs are executed using built-in JavaScript methods.

**Special JavaScript Features/Syntax**

None of the loop constructs use any special JavaScript features or syntax beyond what's described above.

**Alternatives**

If you're looking for alternatives to these loop constructs, consider the following:

*   **`while` loops**: Can be used as an alternative to `for` loops when iterating over arrays.
*   **`Array.prototype.forEach()` with a callback function**: Can be used as an alternative to `forEach`.
*   **Lodash's `map()`, `filter()`, and `reduce()` functions**: Can be used as alternatives to certain loop constructs, such as filtering or mapping an array.

In conclusion, the benchmark provides a comprehensive comparison of different loop constructs in JavaScript. Understanding the pros and cons of each approach can help developers make informed decisions about which method to use for specific tasks.

Related benchmarks:

for vs for (reverse with length) vs every vs forEach with big array 2 (version: 0)

Comparing performance of: for vs for (reverse with length) vs some vs every vs forEach

Created: 3 years ago by: Guest

Jump to the latest result

for

for (reverse with length)

some

every

forEach

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 5 months ago):