Benchmark: CompareFor20190430

Script Preparation code:

var saved = new Array(1000).fill(null).map((v, item) => ({item}));

Tests:

for
var savedMap = {}; for (var i = 0; i < saved.length; i++) { savedMap[saved[i].item] = saved[i]; }
forEach
var savedMap = {}; saved.forEach(item => { savedMap[item.item] = item; });
for optimized 1
var savedMap = {}; for (var i = 0, l = saved.length; i < l; i++) { savedMap[saved[i].item] = saved[i]; }
for optimized 2
var savedMap = {}; for (var i = 0, l = saved.length; i < l; i++) { var item = saved[i]; savedMap[item.item] = item; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
for
forEach
for optimized 1
for optimized 2

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: one year ago)

User agent: Mozilla/5.0 (iPhone; CPU iPhone OS 18_2 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/18.2 Mobile/15E148 Safari/604.1

Browser/OS: Mobile Safari 18 on iOS 18.2

View result in a separate tab

Test name	Executions per second
for	113325.4 Ops/sec
forEach	101821.7 Ops/sec
for optimized 1	110305.8 Ops/sec
for optimized 2	109925.6 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 provided benchmark and explain what's being tested, compared, and some pros/cons of each approach.

**Benchmark Overview**

The benchmark compares three different ways to iterate over an array in JavaScript:

1. Traditional `for` loop
2. `forEach` method
3. Optimized `for` loops (with and without a separate variable for the item)

**Test Case 1: Traditional `for` Loop**

The benchmark definition uses:
```javascript
var savedMap = {};
for (var i = 0; i < saved.length; i++) {
  savedMap[saved[i].item] = saved[i];
}
```
This is a classic `for` loop that iterates over the array using an index variable `i`. The pros of this approach are:

* Simple and easy to understand
* Works in most browsers

However, this approach has some cons:

* Slow performance due to the overhead of incrementing the index variable
* May not be as efficient as other approaches for large arrays

**Test Case 2: `forEach` Method**

The benchmark definition uses:
```javascript
var savedMap = {};
saved.forEach(item => {
  savedMap[item.item] = item;
});
```
The `forEach` method is a built-in array method that iterates over the array using a callback function. The pros of this approach are:

* Fast performance due to optimized iteration implementation
* Does not require manual index management

However, this approach has some cons:

* May not work in older browsers or environments that do not support `forEach`
* Does not provide direct access to the index variable (in this case, it's implicit)

**Test Case 3: Optimized `for` Loop**

The benchmark definition uses:
```javascript
var savedMap = {};
for (var i = 0, l = saved.length; i < l; i++) {
  // do nothing with i
}
```
This is an optimized version of the traditional `for` loop. By removing the unnecessary increment of the index variable, this approach can be faster than the original.

The pro of this approach are:

* Fast performance due to reduced overhead

However, this approach has some cons:

* May not work in older browsers or environments that do not support optimized loops
* Does not provide direct access to the item being processed (in this case, it's implicit)

**Test Case 4: Optimized `for` Loop with Separate Variable**

The benchmark definition uses:
```javascript
var savedMap = {};
for (var i = 0, l = saved.length; i < l; i++) {
  var item = saved[i];
  savedMap[item.item] = item;
}
```
This is another optimized version of the traditional `for` loop. By assigning the current item to a separate variable, this approach can be faster and more efficient.

The pros of this approach are:

* Fast performance due to reduced overhead
* Provides direct access to the item being processed

However, this approach has some cons:

* May not work in older browsers or environments that do not support optimized loops
* Requires manual index management (which may be slower for large arrays)

**Library Used: None**

There is no library used in these benchmark definitions. The `forEach` method is a built-in array method, and the other approaches use basic JavaScript constructs like `for` loops.

**Special JS Feature/Syntax: None**

There are no special features or syntax used in these benchmark definitions.

**Other Alternatives**

Some alternative approaches to iterate over an array in JavaScript include:

* Using `while` loops instead of `for` loops
* Using recursion to iterate over the array
* Using a custom implementation using bitwise operators (e.g., using `shift()` and `unshift()` methods)

However, these alternatives may not be as efficient or well-supported as the built-in methods used in this benchmark.

Related benchmarks:

CompareFor20190430 (version: 2)

Comparing performance of: for vs forEach vs for optimized 1 vs for optimized 2

Created: 7 years ago by: Registered User

Jump to the latest result

for

forEach

for optimized 1

for optimized 2

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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