Benchmark: Map vs For Loop - MeasureThat.net

Script Preparation code:

var a = new Array(1e6);
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; }
For Loop -- Cached array length
var b = []; var len = a.length; for (var i = 0; i < len; i++) { b[i] = a[i] * 2; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Map
For Loop
For Loop -- Cached array length

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 7 years ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:52.0) Gecko/20100101 Firefox/52.0

Browser/OS: Firefox 52 on Mac OS X 10.12

View result in a separate tab

Test name	Executions per second
Map	164.2 Ops/sec
For Loop	85.8 Ops/sec
For Loop -- Cached array length	120.9 Ops/sec

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

LLMs can make mistakes. Check important info.

**Benchmark Overview**

The provided benchmark compares the performance of two approaches to iterate over an array in JavaScript: using the `map()` method and traditional for loops.

**Script Preparation Code**

The script preparation code generates an array `a` with 1 million elements, populating it with random values. This is done using a traditional for loop:

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

**Html Preparation Code**

There is no HTML preparation code provided.

**Individual Test Cases**

The benchmark consists of three test cases, each representing a different approach to iterate over the array:

1. **Map**: The `map()` method is used to create a new array `b` with the same elements as `a`, but with each element multiplied by 2.
```javascript
var b = a.map(n => n * 2);
```
2. **For Loop**: A traditional for loop is used to iterate over the elements of `a` and populate `b`.
```javascript
for (i = 0; i < a.length; i++) {
  b[i] = a[i] * 2;
}
```
3. **For Loop -- Cached array length**: The same as the previous test case, but with the array length cached outside of the loop.
```javascript
var len = a.length;
for (i = 0; i < len; i++) {
  b[i] = a[i] * 2;
}
```
**Pros and Cons**

* **Map**: Pros:
	+ Concise code
	+ Easy to read and maintain
	+ Creates a new array, which can be useful for parallel processing or filtering
* Cons:
	+ May incur overhead due to function call and memory allocation
	+ Can lead to slower performance if the callback function is complex or computationally expensive
* **For Loop**: Pros:
	+ Direct access to array elements
	+ No overhead due to function calls
	+ Easy to optimize for specific use cases (e.g., caching array length)
* Cons:
	+ More verbose code compared to `map()`
	+ Requires manual indexing and bounds checking

**Libraries**

There are no libraries mentioned in the provided benchmark.

**Special JS Features or Syntax**

There are no special JavaScript features or syntax used in this benchmark.

**Other Considerations**

When choosing between these approaches, consider the following factors:

* Code readability and maintainability
* Performance requirements (e.g., iteration speed, parallel processing)
* Memory constraints (e.g., caching array length)

**Alternatives**

If you need to iterate over an array in JavaScript, here are some alternative approaches:

1. **forEach()**: A more concise alternative to traditional for loops.
```javascript
a.forEach((value, index) => {
  // process value
});
```
2. **Reduce()**: A method that applies a callback function to each element of the array and returns a single value.
```javascript
var result = a.reduce((acc, value) => acc + value, 0);
```
3. **filter()** and **some()**: Methods for filtering elements in an array based on a predicate function.
```javascript
const filteredArray = a.filter((value) => /* predicate */);
```

Related benchmarks:

Map vs For Loop (version: 0)

Map vs For Loop with array length cached outside of the loop

Comparing performance of: Map vs For Loop vs For Loop -- Cached array length

Created: 8 years ago by: Registered User

Jump to the latest result

Map

For Loop

For Loop -- Cached array 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):