Benchmark: for vs for...in vs for...of vs forEach

Script Preparation code:

function randNum(max, min) {
	const x = Math.floor(Math.random() * max)
	if (!isFinite(min) && x < min) {
		return min
	}
	return x
}

function randString(max, min, base) {
	let len = randNum(max)
	if (min && len < min) {len = min}
	if (len > max) {len = max}

	let arr = new Uint8Array(len / 2)
	window.crypto.getRandomValues(arr)
	return Array.from(arr, (dec)=> (
		dec.toString(base || 36).padStart(2, '0')
	)).join('')
}

var list = Object.freeze(
	Array(100).map(()=> Object.freeze({
		id: randString(64,64),
		firstName: randString(40,5),
		lastName: randString(40,5),
		email: randString(40,5),
		address: Object.freeze({
			country: randString(40,5),
			state: randString(40,5),
		}),
	}))
)

Tests:

for
for (let i = 0; i < list.length; i++) {const el = list[i]; console.count('for')}
for...in
for (const elIdx in list) {const el = list[elIdx]; console.count('for...in')}
for...of
for (const el of list) {console.count('for...of')}
forEach
list.forEach((el)=> console.count('forEach'))

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

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

Fastest: N/A

Slowest: N/A

Latest run results:

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

User agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36

Browser/OS: Chrome 120 on Linux

View result in a separate tab

for...in

5.7M/s

forEach

1.0M/s

for

3K/s

for...of

3K/s

View exact numbers

Test name	Executions per second
✓ for...in	5,711,178 Ops/sec
forEach	1,042,885 Ops/sec
for	2,526 Ops/sec
for...of	2,500 Ops/sec

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

LLMs can make mistakes. Check important info.

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

**What's being tested:**

The provided benchmark tests four different iteration methods in JavaScript:

1. **Traditional `for` loop**: Iterates over an array using a manual index variable (`i`) that increments on each iteration.
2. **`for...in` loop**: Iterates over an array using the `in` operator, which returns the property names of an object (in this case, the elements of the array).
3. **`for...of` loop**: Iterates over an array using a new syntax that allows iterating directly over the elements of an array without needing to access their indices.
4. **`forEach` method**: A built-in method of arrays that calls a callback function for each element in the array.

**Options compared:**

Each test case compares two or more iteration methods, allowing users to see which one is faster on their system. The comparison options are:

* `for` vs. `for...in` vs. `for...of` vs. `forEach`
* Each pair of methods is tested individually

**Pros and Cons:**

1. **Traditional `for` loop**: Fast, but requires manual index management.
2. **`for...in` loop**: Slow due to property iteration, which can lead to slower performance for large arrays.
3. **`for...of` loop**: Faster than `for...in`, as it uses an optimized iterator that bypasses the property lookup.
4. **`forEach` method**: Fast and convenient, but may incur additional overhead due to the need to call a callback function.

**Special considerations:**

* The benchmark uses randomly generated strings and objects to create a large array (`list`) for testing.
* The `for...in` loop is slower because it needs to iterate over the property names of each object in the array, which can lead to additional overhead.

**Other alternatives:**

If you're interested in exploring other iteration methods or customizing your benchmark, consider using:

1. **`map()` method**: Another built-in method that applies a function to each element in an array.
2. **`reduce()` method**: A built-in method that accumulates values in an array by applying a reduction function.

However, these alternatives are not tested in this benchmark and may produce different results.

Keep in mind that the best iteration method for your use case depends on specific requirements, such as performance, readability, or convenience.

for vs for...in vs for...of vs forEach (version: 3)

Benchmarks the speed of different iteration implementations

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

Created: 3 years ago by: Registered User

Go to the latest result

for

for...in

for...of

forEach

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...in vs for...of vs forEach (version: 3)

Benchmarks the speed of different iteration implementations

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

Created: 3 years ago by: Registered User

Go to the latest result

for

for...in

for...of

forEach

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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

Related benchmarks

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