Benchmark: for vs forEach vs for..in vs for..of (with fixed iterator item reference)

Script Preparation code:

var array = [...Array(1000).keys()];

Tests:

for length
for (var i = 0; i < array.length; i++) { console.log(array[i]); // i is index }
forEach
array.forEach(function(i) { console.log(i); // i is array item });
for..in
for (var i in array) { console.log(array[i]); // i is index }
for..of
for (var i of array) { console.log(i); // i is array item }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
for length
forEach
for..in
for..of

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 27 days ago):

LLMs can make mistakes. Check important info.

Let's break down the provided benchmark and explain what's being tested.

**Benchmark Overview**

The provided benchmark compares the performance of four different loop constructs in JavaScript: `for`, `forEach`, `for...in`, and `for...of`. The goal is to determine which construct is the most efficient for iterating over an array.

**Loop Constructs Compared**

Here's a brief overview of each loop construct being compared:

1. **`for`**: This is a traditional loop construct that uses a variable (`i`) to iterate over the array elements. It checks the condition manually using `array.length`.
2. **`forEach`**: This method is used to execute a function for each element in an array without revealing its internal implementation details. The callback function receives the current element as an argument.
3. **`for...in`**: This loop construct iterates over the enumerable properties of an object (or array) using a variable (`i`) that takes on the property name. Note that `for...in` doesn't directly iterate over arrays, but we're testing it here to see how it performs in this specific context.
4. **`for...of`**: This loop construct is specifically designed for iterating over iterable objects (like arrays). It uses a variable (`i`) that takes on the value of each array element during iteration.

**Library and Special Features**

There's no explicitly mentioned library being used in this benchmark, but we should note that `forEach` relies on the built-in `Array.prototype.forEach()` method, which is not included in this JSON configuration. If it were included, `forEach` would be executed using the provided script preparation code.

**Pros and Cons of Each Approach**

Here's a brief summary of each approach:

1. **`for`**: Simple and straightforward, but it requires manual incrementing of the loop variable (`i`) which can lead to errors if not implemented correctly.
	* Pros: Easy to implement and understand
	* Cons: Error-prone due to manual index management
2. **`forEach`**: This method is designed for high-level iteration and is relatively safe from implementation errors, as it's a standard part of the `Array.prototype`.
	* Pros: Safe and easy to use; built-in to the language
	* Cons: May incur additional overhead due to its abstraction
3. **`for...in`**: Not suitable for array iteration in this context, but can be useful when working with object iteration.
	* Pros: Can iterate over objects (not arrays)
	* Cons: Unnecessary and potentially slower than the correct approach (`for`)
4. **`for...of`**: Specifically designed for array iteration and is often the most efficient option.
	* Pros: Optimized for array iteration; easy to use
	* Cons: May not work as expected if used with non-array iterables

**Other Alternatives**

If this benchmark were to be expanded, other loop constructs could be considered:

1. **`while`**: Another traditional loop construct that can be used for array iteration.
2. **`Array.prototype.reduce()`**: A method that can be used for accumulation-based array operations.
3. **`setInterval()`** or **`requestAnimationFrame()`**: For more complex scenarios where iterative loops are not the best fit.

Please let me know if you have any further questions!

Latest run results:

Run details: (Test run date: one year ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/112.0.0.0 Safari/537.36

Browser/OS: Chrome 112 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
for length	337.9 Ops/sec
forEach	319.0 Ops/sec
for..in	315.3 Ops/sec
for..of	273.4 Ops/sec

Related benchmarks:

for vs forEach vs for..in vs for..of (with fixed iterator item reference) (version: 0)

Compare loop performance

Comparing performance of: for length vs forEach vs for..in vs for..of

Created: one year ago by: Guest

Jump to the latest result

for length

forEach

for..in

for..of

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 27 days ago):