Benchmark: Map vs Foreach mutate array

Script Preparation code:

var largeArray = Array(1000000).fill('x');

Tests:

Map
largeArray = largeArray.map( (value) => { return value+'y';});
Foreach
largeArray.forEach((value, index) => { largeArray[index] = value +'y'; });

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Map
Foreach

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 28 days ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:149.0) Gecko/20100101 Firefox/149.0

Browser/OS: Firefox 149 on Windows

View result in a separate tab

Test name	Executions per second
Map	18.7 Ops/sec
Foreach	4.1 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 JSON data to understand what is being tested in this JavaScript microbenchmark.

**Benchmark Overview**

The benchmark, titled "Map vs Foreach mutate array", aims to compare the performance of two approaches on modifying an array: `map()` and `forEach()`. The test uses a large array (1 million elements) filled with the string 'x' as input data.

**Options Compared**

Two options are being compared:

1. **`map()`**: This is a method that returns a new array created by calling a provided function for each element in the original array.
2. **`forEach()`**: This is a method that executes an anonymous function on every element in the array, but does not return a new value.

**Pros and Cons**

* **`map()`**:
	+ Pros: It returns a new array with modified values, which can be useful for many applications (e.g., data transformation).
	+ Cons: It creates a new array object, which can lead to increased memory allocation and garbage collection overhead.
* **`forEach()`**:
	+ Pros: It modifies the original array, which can be beneficial when you need to keep the modified array unchanged elsewhere in your codebase.
	+ Cons: It does not return a new value, so its result is discarded after execution.

In terms of performance, `map()` is generally expected to be faster than `forEach()`, as it only requires iterating over the input array once and returning a new value, whereas `forEach()` also needs to update the original array with modified values.

**Library and Special JS Feature**

Neither `map()` nor `forEach()` relies on any external libraries. However, both methods are supported by most modern JavaScript engines, including those used by Chrome 84, as indicated in the latest benchmark result.

**Other Considerations**

* Memory usage: Both methods can lead to increased memory allocation, especially when dealing with large arrays.
* Caching: Some JavaScript engines may cache results for subsequent invocations of `map()` or `forEach()`, which could affect performance and accuracy of the benchmark.
* Modern browsers often use optimizations such as array caching, SIMD (Single Instruction, Multiple Data) instructions, or even compiler-based optimizations to improve performance.

**Alternative Approaches**

Other methods that can be used to modify arrays include:

1. **`reduce()`**: Like `map()`, it returns a new array created by applying a reduction function to each element.
2. **`filter()`**: Returns a new array containing elements from the original array for which the filter callback returns true.

However, these methods may not be as straightforward or efficient as `map()` and `forEach()`. The choice of method depends on the specific use case and performance requirements.

In summary, this benchmark compares the performance of two common JavaScript array modification methods: `map()` and `forEach()`. While both have their pros and cons, `map()` is generally expected to be faster due to its ability to return a new value.

Related benchmarks:

Map vs Foreach mutate array (version: 0)

This test will run map, vs foreach on a larger array and make sure you get a modified array

Comparing performance of: Map vs Foreach

Created: 5 years ago by: Registered User

Jump to the latest result

Map

Foreach

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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