Benchmark: for vs while vs for of vs forEach（optimaized

Script Preparation code:

var arr = []
for (var i = 0; i < 1000; i++) arr[i] = i

Tests:

for i++
var l = arr.length for (var i = 0; i < l; i++) { var a = arr[i] }
for i--
for (var i = arr.length; i >= 0; i--) { var a = arr[i] }
while i--
var i = arr.length while (i--) { var a = arr[i] }
for of
for (var v of arr) { var a = v }
forEach
arr.forEach(v => { var a = v })

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
for i++
for i--
while i--
for of
forEach

Fastest: N/A

Slowest: N/A

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/126.0.0.0 Safari/537.36

Browser/OS: Chrome 126 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
for i++	30263.5 Ops/sec
for i--	30372.8 Ops/sec
while i--	29740.0 Ops/sec
for of	2729405.5 Ops/sec
forEach	2744189.2 Ops/sec

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

LLMs can make mistakes. Check important info.

I'll break down the provided benchmark JSON and explain what's being tested, compared, and their pros and cons.

**Benchmark Overview**

The benchmark measures the performance of different loops in JavaScript: traditional `for`, `while` with post-decrement (`i--`), `for...of` (introduced in ECMAScript 2015), and `forEach`. The test cases aim to iterate over an array of length 1000, accessing each element using a variable `a`.

**Test Cases**

Each test case has a unique loop construct being compared. Here's a brief explanation:

1. **Traditional `for` loop**: Iterates from index 0 to the length of the array.
2. **Post-decrement `while` loop (`i--`)**: Decrementing the index in each iteration, starting from the length of the array.
3. **`for...of` loop**: Iterates over the elements of an iterable (in this case, an array) using a "foreach" syntax.
4. **`forEach` function**: Calls a callback function for each element in an array.

**Comparison and Performance**

The benchmark measures the number of executions per second (`ExecutionsPerSecond`) for each loop construct on a Chrome 126 browser on a Mac OS X 10.15.7 device. The results show that:

* `for...of` is generally faster than traditional `for` loops.
* Post-decrement `while` loops are slower than both traditional `for` and `for...of` loops.

**Pros and Cons**

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

1. **Traditional `for` loop**: Pros:
	* Well-established, widely supported syntax.
	* Easy to understand and use.
2. **Post-decrement `while` loop (`i--`)**: Cons:
	* Requires careful indexing to avoid off-by-one errors.
	* Can be slower than other options due to the increment/decrement operation.
3. **`for...of` loop**: Pros:
	+ More modern and efficient syntax.
	+ Encourages a more "iterative" mindset.
4. **`forEach` function**: Pros:
	+ Concise and expressive syntax for iterating over arrays.

**Other Alternatives**

While not part of the benchmark, other loop constructs in JavaScript include:

* `while` loops with pre-decrement (`i--`) or pre-increment (`++i`).
* Array methods like `map()`, `filter()`, and `reduce()`.
* Generators and iterators for more complex iteration scenarios.

Keep in mind that this benchmark focuses on the relative performance of different loop constructs, rather than their suitability for specific use cases.

Related benchmarks:

for vs while vs for of vs forEach（optimaized (version: 0)

Comparing performance of: for i++ vs for i-- vs while i-- vs for of vs forEach

Created: one year ago by: Guest

Jump to the latest result

for i++

for i--

while i--

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):