Benchmark: forEach vs for each vs for of vs for let

Script Preparation code:

var count = 100000
var arr = Array.from({length: count});

Tests:

traditional
for(let i=0; i<count; i++){ const x = i; }
array method
arr.forEach(r => { const x = i; })
of
for (let each of arr) { const x = each; }
in
for (let each in arr) { const x = each; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
traditional
array method
of
in

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
traditional	307.9 Ops/sec
array method	25759.3 Ops/sec
of	18716.0 Ops/sec
in	415.0 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's break down what is being tested in this benchmark.

**Script Preparation Code**

The script preparation code sets up the test environment by creating an array of length 100,000 and assigning it to a variable named `arr`.

```javascript
var count = 100000;
var arr = Array.from({length: count});
```

This creates an array that is large enough to cause significant performance differences between different iteration methods.

**Test Cases**

There are four test cases:

1. **Traditional Loop**
```javascript
for(let i=0; i<count; i++) {
  const x = i;
}
```
This is a traditional loop using a `for` loop with an index variable `i`.

2. **Array Method**
```javascript
arr.forEach(r => {
  const x = i;
})
```
This uses the `forEach` method of the array to iterate over its elements.

3. **Of Loop**
```javascript
for (let each of arr) {
  const x = each;
}
```
This is an example of a "of" loop, which was introduced in ECMAScript 2019 as part of the Object First engine. This type of loop iterates over the elements of an array using a foreach-like syntax.

4. **In Loop**
```javascript
for (let each in arr) {
  const x = each;
}
```
This is a traditional `for...in` loop that iterates over the properties of an object, including arrays.

**Comparison**

The benchmark compares the performance of these four iteration methods on a large array. The results will likely show significant differences between them due to their different syntax and implementation details.

**Pros and Cons**

Here are some pros and cons of each approach:

* **Traditional Loop**: Pros: widely supported, easy to understand. Cons: can be slow for large arrays, may have performance issues with certain data types.
* **Array Method**: Pros: concise, modern syntax. Cons: may not work in older browsers or environments that don't support `forEach`.
* **Of Loop**: Pros: concise, modern syntax. Cons: may not work in older browsers or environments that don't support "of" loops.
* **In Loop**: Pros: can be used for iterating over objects with inherited properties. Cons: can be slow and confusing to use.

**Library/Functionality**

None of the test cases use a specific library or functionality, they only rely on built-in JavaScript features.

**Special JS Features/Syntax**

Only one special feature is used in this benchmark:

* **ECMAScript 2019 "of" loop**: This is a new type of loop introduced in ECMAScript 2019 that iterates over the elements of an array using a foreach-like syntax. It's not widely supported yet and may require specific browsers or environments to work.

**Alternatives**

Other alternatives for iterating over arrays include:

* Using `map()`, `filter()`, and other array methods instead of loops.
* Using `while` loops with indices, which can be more efficient than traditional `for` loops.
* Using functional programming techniques like reducing functions or using `reduce()`.

Note that the best approach will depend on the specific requirements of the use case and the performance characteristics of the data being iterated over.

Related benchmarks:

forEach vs for each vs for of vs for let (version: 1)

Comparing performance of: traditional vs array method vs of vs in

Created: one year ago by: Registered User

Jump to the latest result

traditional

array method

of

in

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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