Benchmark: for-in vs foreach vs for-of

Script Preparation code:

var array = new Array(100);

Tests:

for-in
for (var i = 0; i < array.length; ++i) { array[i]; }
foreach
array.forEach((item) => { item; });
for-of
for (const item of array) { item; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
for-in
foreach
for-of

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/130.0.0.0 Safari/537.36

Browser/OS: Chrome 130 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
for-in	219625.2 Ops/sec
foreach	9153500.0 Ops/sec
for-of	22089778.0 Ops/sec

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

LLMs can make mistakes. Check important info.

**Overview of the Benchmark**

The provided JSON represents a JavaScript benchmarking test case, specifically comparing the performance of three different loop iteration methods: `for-in`, `foreach` (or `forEach`), and `for-of`. The benchmark is designed to measure which method is the most efficient in terms of speed.

**Loop Iteration Methods Comparison**

1. **For-In Loop**: This method uses a traditional `for` loop with an index variable, similar to the classic C-style loops. It checks each element in the array using the `in` keyword and increments the index manually.
```javascript
for (var i = 0; i < array.length; ++i) {
  array[i];
}
```
**Pros:**

* Easy to understand and implement
* Works on older browsers that don't support newer loop syntax

**Cons:**

* Slow due to manual index incrementing
* Less efficient than other methods

2. **Foreach Loop (or forEach)**: This method uses the `forEach` function, which is a built-in JavaScript function for iterating over arrays. It takes a callback function that executes once for each element in the array.
```javascript
array.forEach((item) => {
  item;
});
```
**Pros:**

* Fast and efficient due to optimized native code
* Easy to read and understand

**Cons:**

* May not be compatible with older browsers (before Chrome 10)
* Less control over iteration compared to other methods

3. **For-Of Loop**: This method uses a new loop syntax introduced in ECMAScript 2015 (ES6). It allows iterating over arrays using a `for` loop with a `const` variable that takes the values from the array.
```javascript
for (const item of array) {
  item;
}
```
**Pros:**

* Fast and efficient due to optimized native code
* Easy to read and understand
* Compatible with modern browsers

**Library Used**

None.

**Special JS Features or Syntax**

No special features or syntax are used in this benchmark, apart from the newer `for-of` loop introduced in ES6. The benchmark is designed to be language-agnostic, making it compatible with a wide range of JavaScript engines and versions.

**Other Alternatives**

Some alternative loop iteration methods that could have been included in this benchmark are:

* **Array.prototype.forEach.call()**: This method uses the `forEach` function and calls it on an array-like object.
```javascript
array.forEach.call(array, (item) => {
  item;
});
```
* **Map iterations**: Some JavaScript engines support iterating over maps using a `for...in` loop, similar to arrays.
* **Array.prototype.entries()**: This method returns an iterator for the elements of an array.

However, these alternatives are not as commonly used or well-supported as the three methods mentioned in this benchmark.

Related benchmarks:

for-in vs foreach vs for-of (version: 0)

Compare loop performance

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

Created: 3 years ago by: Guest

Jump to the latest result

for-in

foreach

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):