Benchmark: Map vs For Loop - MeasureThat.net

Script Preparation code:

var a = [];
for (var i = 0; i < 1e6; i++) {
  a[i] = Math.random();
}

Tests:

Map
var b = a.map(n => n * 2);
For Loop
var b = []; for (var i = 0; i < a.length; i++) { b[i] = a[i] * 2; }
foreach
var b = a.forEach(n => n * 2);
pre-allocated for loop
var b = new Array(a.length); for (var i = 0; i < a.length; i++) { b[i] = a[i] * 2; }
pre-allocated unrolled for loop
var b = new Array(a.length); for (var i = 0; i < a.length/4; i++) { b[i*4] = a[i*4] * 2; b[i*4+1] = a[i*4+1] * 2; b[i*4+2] = a[i*4+2] * 2; b[i*4+3] = a[i*4+3] * 2; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Map
For Loop
foreach
pre-allocated for loop
pre-allocated unrolled for loop

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 26 days ago):

LLMs can make mistakes. Check important info.

Let's dive into the world of JavaScript microbenchmarks on MeasureThat.net.

**Benchmark Overview**

The provided benchmark compares four approaches to multiply an array by 2:

1. `map()`
2. Traditional `for` loop
3. Pre-allocated `for` loop
4. Pre-allocated and unrolled `for` loop

We'll break down each approach, its pros and cons, and discuss any notable libraries or JavaScript features used.

**Approach 1: Map**

The first approach uses the `map()` method to multiply each element of the array `a` by 2.
```javascript
var b = a.map(n => n * 2);
```
Pros:

* Concise and expressive code
* No need to worry about indexing or bounds checking

Cons:

* Creates a new array, which may lead to memory allocation overhead for large arrays.
* May not be as efficient as other approaches for very large arrays.

**Approach 2: Traditional For Loop**

The second approach uses a traditional `for` loop to iterate over the elements of the array `a` and multiply each element by 2.
```javascript
var b = [];
for (var i = 0; i < a.length; i++) {
  b[i] = a[i] * 2;
}
```
Pros:

* Can be more efficient than `map()` for very large arrays, as it avoids the memory allocation overhead of creating a new array.
* Allows for direct access to elements without bounds checking.

Cons:

* Requires manual indexing and bounds checking, which can lead to errors.
* Less concise and less expressive code compared to `map()`.

**Approach 3: Pre-allocated For Loop**

The third approach pre-allocation initializes an empty array `b` with the same length as `a`, and then uses a traditional `for` loop to populate it.
```javascript
var b = new Array(a.length);
for (var i = 0; i < a.length; i++) {
  b[i] = a[i] * 2;
}
```
Pros:

* Reduces memory allocation overhead compared to `map()`, as the array is pre-allocated.
* Allows for direct access to elements without bounds checking.

Cons:

* Requires manual indexing and bounds checking, which can lead to errors.
* Less concise and less expressive code compared to `map()`.

**Approach 4: Pre-allocated and Unrolled For Loop**

The fourth approach combines the benefits of pre-allocation and unrolling the loop. It initializes an empty array `b` with the same length as `a`, and then uses a traditional `for` loop to populate it in an unrolled manner (i.e., four elements are processed together).
```javascript
var b = new Array(a.length);
for (var i = 0; i < a.length/4; i++) {
  b[i*4] = a[i*4] * 2;
  b[i*4+1] = a[i*4+1] * 2;
  b[i*4+2] = a[i*4+2] * 2;
  b[i*4+3] = a[i*4+3] * 2;
}
```
Pros:

* Reduces memory allocation overhead compared to `map()`, as the array is pre-allocated.
* Allows for direct access to elements without bounds checking.

Cons:

* Requires manual indexing and bounds checking, which can lead to errors.
* Less concise and less expressive code compared to `map()`.

**Library: None**

None of the approaches rely on any external libraries.

**Special JavaScript Feature: none**

None of the approaches use special JavaScript features like `let` or `const` variables.

Now that we've discussed each approach, let's talk about other alternatives:

* **Splice()**: Instead of using `map()` or traditional loops, you can use `splice()` to modify the original array.
* **Array.prototype.forEach()**: Another alternative to `map()` is using `forEach()` with a callback function.

Keep in mind that these alternatives may have different performance characteristics and trade-offs compared to the approaches discussed above.

Latest run results:

Run details: (Test run date: 8 months ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/122.0.0.0 Safari/537.36

Browser/OS: Chrome 122 on Windows

View result in a separate tab

Test name	Executions per second
Map	12.8 Ops/sec
For Loop	7.7 Ops/sec
foreach	93.2 Ops/sec
pre-allocated for loop	8.7 Ops/sec
pre-allocated unrolled for loop	13.5 Ops/sec

Related benchmarks:

Map vs For Loop (version: 0)

Comparing performance of: Map vs For Loop vs foreach vs pre-allocated for loop vs pre-allocated unrolled for loop

Created: 7 years ago by: Guest

Jump to the latest result

Map

For Loop

foreach

pre-allocated for loop

pre-allocated unrolled for loop

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 26 days ago):