Benchmark: for vs foreach vs for..in vs for..of (Fixed)

Script Preparation code:

var array = new Array(100);

Tests:

for
for (let i = 0, len = array.length; i < len; i++) { array[i]; }
foreach
array.forEach(function(i) { i; });
for in
for (let i in array) { array[i]; }
for..of
for (let i of 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: 2 days ago)

User agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/135.0.0.0 Safari/537.36

Browser/OS: Chrome 135 on Linux

View result in a separate tab

Test name	Executions per second
for	9790689.0 Ops/sec
foreach	10801020.0 Ops/sec
for in	7865388.0 Ops/sec
for..of	40023508.0 Ops/sec

Autogenerated LLM Summary (model gpt-4o-mini, generated 2 days ago):

LLMs can make mistakes. Check important info.

The provided benchmark focuses on evaluating the performance of different looping constructs in JavaScript: `for`, `forEach`, `for..in`, and `for..of`. Each of these constructs serves the purpose of iterating over arrays or collections, but they differ in syntax, performance characteristics, and appropriate use cases.

### 1. Loop Constructs Compared

- **for loop**: 
  ```javascript
  for (let i = 0, len = array.length; i < len; i++) {
    array[i];
  }
  ```
  *Pros*: 
  - Highly efficient for array traversal as it has minimal overhead; direct access to elements.
  - Allows more control over iteration (e.g., breaking the loop, modifying the loop variable).

*Cons*: 
  - More verbose and requires manual management of the loop index and length.

- **forEach method**: 
  ```javascript
  array.forEach(function(i) {
    i;
  });
  ```
  *Pros*: 
  - Provides a more readable and declarative syntax, allows function abstraction.
  - Automatically manages loop iterations.

*Cons*: 
  - Slightly slower than a traditional `for` loop due to function call overhead.
  - Cannot use `break` or `continue` statements to control iteration flow.

- **for..in loop**: 
  ```javascript
  for (let i in array) {
    array[i];
  }
  ```
  *Pros*: 
  - Useful for looping through object properties (including object keys).

*Cons*: 
  - Not recommended for arrays due to potential iteration over inherited properties and non-numeric keys.
  - Performance is generally subpar compared to other loop constructs.

- **for..of loop**: 
  ```javascript
  for (let i of array) {
    i;
  }
  ```
  *Pros*: 
  - More modern and cleaner syntax for runtime iteration over iterable objects (including arrays).
  - Automatically skips non-numeric properties and inherited properties.

*Cons*: 
  - Slightly slower than traditional `for` loops but more efficient than `forEach`.

### 2. Performance Results

Based on the latest benchmark results, the `for..of` loop showed the highest performance with **40,023,508 executions per second**, followed by `forEach` at **10,801,020**. The traditional `for` loop performed at **9,790,689**, and the `for..in` loop had the lowest performance at **7,865,388** executions per second.

### 3. Considerations and Alternative Approaches

When choosing a loop construct, developers often consider the following:

- **Readability vs. Performance**: For performance-critical code, a traditional `for` or `for..of` loop could be preferred. In less performance-sensitive contexts, `forEach` may be chosen for its readability.
- **Mutation**: If the loop needs to break, return early, or modify the original array, a standard `for` loop is typically a better choice.
- **Iterability**: If working with structures other than arrays (like Sets or Maps), `for..of` is a strong choice due to its compatibility with any iterable.
  
### 4. Alternatives

Other alternatives for loop constructs include:

- **Map and Reduce methods**: These carry out transformations or calculations on arrays and can result in more concise code, but they can introduce overhead compared to traditional loops.
- **`while` loop**: Offers another control structure that can be used for iteration, but manually managing the loop condition can add complexity and risk for errors.
- **List comprehensions (in Python)**: While not applicable in JavaScript, similar constructs found in other languages improve readability and efficiency, highlighting a need for comparable functionality or syntactic sugar in JavaScript.

In summary, the choice of loop construct is context-dependent and should be made considering performance, readability, and requirements of the specific task at hand.

Related benchmarks:

for vs foreach vs for..in vs for..of (Fixed) (version: 1)

Compare loop performance

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

Created: 2 days ago by: Guest

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for

foreach

for in

for..of

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model gpt-4o-mini, generated 2 days ago):