Benchmark: for (cache length) vs foreach vs for..in vs for..of

Script Preparation code:

var array = new Array(100);

Tests:

for
var arrLength = array.length; for (var i = 0; i < arrLength; i++) { array[i]; }
foreach
array.forEach(function(i) { array[i]; });
for in
for (var i in array) { array[i]; }
for..of
for (var i of array) { array[i]; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

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

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 9 days ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) Brave/1 Version/26.4 Safari/605.1.15

Browser/OS: Safari 26 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
for	348992.6 Ops/sec
foreach	444478.2 Ops/sec
for in	7160882.5 Ops/sec
for..of	203755.6 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 benchmark and its test cases.

**Benchmark Definition:**
The benchmark is designed to compare the performance of four different loop types in JavaScript:

1. `for` loop
2. `forEach` loop (a part of the Array prototype)
3. `for...in` loop (an older way of looping through arrays, using the `in` keyword)
4. `for...of` loop (a newer way of looping through arrays and other iterable objects, introduced in ECMAScript 2015)

**Options Compared:**
The benchmark is comparing the performance of these four loop types on a fixed input: an array of length 100.

**Pros and Cons:**

* **`for` loop:** Simple, efficient, and widely supported. However, it can be less readable for some developers who are not familiar with its syntax.
* **`forEach` loop:** More modern and concise than `for` loops, but can be slower due to the overhead of the callback function. It's also less flexible, as it only allows a single callback function to be executed.
* **`for...in` loop:** Less efficient than `for` loops and `forEach` loops, especially for large arrays. This is because `for...in` requires the browser to iterate through the array's prototype chain, which can slow down the execution.
* **`for...of` loop:** More efficient than `for` loops and `forEach` loops, as it allows for direct access to array elements without the need for indexing or callbacks. It's also more readable and concise.

**Library Used:**
None explicitly mentioned in the benchmark definition, but `forEach` is a part of the Array prototype, which is a built-in JavaScript library.

**Special JS Feature/Syntax:**
The `for...of` loop uses a new syntax introduced in ECMAScript 2015. This loop type allows for direct access to iterable objects' elements without needing indexing or callbacks. The browser's implementation of this feature may vary, which can affect performance.

**Other Considerations:**

* **Browser support:** The benchmark results are from Chrome 115 on a desktop platform. Browser support and performance may vary across different browsers, operating systems, and devices.
* **Optimization opportunities:** The benchmark does not consider optimization techniques such as loop unrolling, caching, or SIMD instructions, which can further improve performance.

**Alternatives:**

* Other loop types, such as `while` loops or `for-each` loops in other programming languages (e.g., Python's `enumerate()` function).
* Performance profiling tools and libraries that can help identify bottlenecks and optimize code for specific use cases.
* Specialized JavaScript frameworks or libraries designed to improve performance, such as WebAssembly or Just-In-Time (JIT) compilers.

Related benchmarks:

for (cache length) vs foreach vs for..in vs for..of (version: 0)

Compare loop performance

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

Created: 2 years ago by: Guest

Jump to the latest result

for

foreach

for in

for..of

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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