Benchmark: for vs foreach vs some vs for..of vs for cached length

Script Preparation code:

var array = new Array(1000);

Tests:

for
for (var i = 0; i < array.length; i++) { array[i]; }
foreach
array.forEach(function(i) { array[i]; });
some
array.some(function(i) { array[i]; });
for..of
for (var i of array) { array[i]; }
for cached length
for (var i = 0, l=array.length; i < l; ++i) { array[i]; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
for
foreach
some
for..of
for cached length

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 3 years ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Firefox/78.0

Browser/OS: Firefox 78 on Windows

View result in a separate tab

Test name	Executions per second
for	125156.8 Ops/sec
foreach	986749.8 Ops/sec
some	1077035.9 Ops/sec
for..of	10113.7 Ops/sec
for cached length	289782.5 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's break down the provided benchmark and explain what's being tested, compared, and analyzed.

**Benchmark Overview**

The benchmark compares the performance of four different loop constructs in JavaScript:

1. Traditional `for` loop
2. `forEach` method (a part of the Array API)
3. `some` method (also a part of the Array API)
4. `for..of` loop (introduced in ECMAScript 2015)

**Loop Constructs**

Let's examine each loop construct:

1. **Traditional `for` loop**: A classic, manually managed loop where the index is incremented or decremented.
```javascript
for (var i = 0; i < array.length; i++) {
    array[i];
}
```
Pros: Simple and familiar to many developers.
Cons: Manual index management can lead to bugs.

2. **`forEach` method**: An iterator-based loop that executes a callback function for each element in the array.
```javascript
array.forEach(function(i) {
    array[i];
});
```
Pros: Easy to use, minimal code required.
Cons: May not be as efficient as traditional loops, especially for small arrays.

3. **`some` method**: A short-circuiting loop that returns a boolean value indicating whether at least one element in the array passes a test.
```javascript
array.some(function(i) {
    array[i];
});
```
Pros: Can be useful when only one condition needs to be met.
Cons: May not be suitable for all use cases, as it short-circuits.

4. **`for..of` loop**: A modern, iterator-based loop that executes a block of code for each element in the array.
```javascript
for (var i of array) {
    array[i];
}
```
Pros: Concise and easy to read, with minimal boilerplate code.
Cons: May not be as well-supported by older browsers or versions.

**Cache-Friendly `for` loop**

The "cached length" version of the traditional `for` loop uses a cached reference to the array's length property:
```javascript
for (var i = 0, l=array.length; i < l; ++i) {
    array[i];
}
```
Pros: Can be faster for large arrays due to reduced overhead.
Cons: Requires manual index management and cache maintenance.

**Other Considerations**

* **Performance**: The benchmark measures the number of executions per second (ExecutionsPerSecond) for each loop construct. This metric provides a general idea of performance, but may not account for other factors like memory usage or thread safety.
* **Browser Support**: The benchmark uses Firefox 78 as the reference browser, which means results may vary across different browsers and versions.
* **Array Size**: The array size is fixed at 1000 elements, which might be too small to capture performance differences for very large arrays.

**Alternatives**

If you're looking for alternative loop constructs or optimizations, consider:

* **`while` loops**: A more flexible option when the number of iterations isn't known.
* **Array.prototype.map()`, `Array.prototype.filter()`, and `Array.prototype.reduce()` methods: Can be used to perform operations on arrays without manual indexing.
* **Generator functions**: Can provide a concise way to iterate over large datasets while maintaining memory efficiency.

Keep in mind that the best loop construct depends on your specific use case, performance requirements, and personal preference.

Related benchmarks:

for vs foreach vs some vs for..of vs for cached length (version: 0)

Compare loop performance

Comparing performance of: for vs foreach vs some vs for..of vs for cached length

Created: 3 years ago by: Guest

Jump to the latest result

for

foreach

some

for..of

for cached length

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

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