Benchmark: Javascript concat vs concat with ES6 spread vs ES6 construction with ES6 spread

Script Preparation code:

var arr1 = [];
var arr2 = [];
for (var i=0; i<1000; i++){
  arr1.push(i);
  arr2.push(i);
}

Tests:

Concat
arr1.concat(arr2)
Concat with spread
arr1.concat(...arr2)
ES6 construction with spreads
[...arr1, ...arr2]

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Concat
Concat with spread
ES6 construction with spreads

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 24 days ago):

LLMs can make mistakes. Check important info.

Let's break down the JavaScript benchmark and explain what's being tested, the different approaches compared, their pros and cons, and other considerations.

**Benchmark Overview**

The benchmark compares three ways to concatenate two arrays in JavaScript: using `concat()`, `...` spread operator (also known as "spread syntax"), and ES6 construction with `Array.from()`.

**Script Preparation Code**

The script preparation code creates two empty arrays, `arr1` and `arr2`, and then populates them with 1000 elements each using a `for` loop. This setup is used to ensure that the benchmark measures the performance of the concatenation operations in isolation.

**Individual Test Cases**

There are three test cases:

1. **Concat**: This test case measures the performance of `arr1.concat(arr2)`.
2. **Concat with spread**: This test case measures the performance of `arr1.concat(...arr2)`, which uses the spread operator to concatenate the arrays.
3. **ES6 construction with spreads**: This test case measures the performance of `[...arr1, ...arr2]`, which uses ES6's spread syntax to create a new array and then concatenates it.

**Library**

None of these benchmark cases use any external libraries.

**Special JS Features or Syntax**

* The `...` spread operator is used in two test cases (`Concat with spread` and `ES6 construction with spreads`). This is a relatively recent addition to JavaScript (introduced in ECMAScript 2015) that allows for concise array concatenation.
* ES6's `Array.from()` method is not used in any of the benchmark cases, but it's worth noting that this method can also be used to concatenate arrays.

**Pros and Cons**

Here are some pros and cons of each approach:

1. **Concat**: This is a simple and widely supported way to concatenate arrays. However, it creates a new array object and copies all elements from the original arrays into the new one, which can be inefficient for large datasets.
2. **Concat with spread**: Using the spread operator can make the code more concise and easier to read. It also avoids creating a new array object, as the concatenation happens directly on the original arrays. However, some older browsers may not support this syntax.
3. **ES6 construction with spreads**: This approach creates a new array using `Array.from()` and then concatenates it with the spread operator. While it's more efficient than using `concat()`, it may not be as readable or concise as the other approaches.

**Other Considerations**

* The benchmark uses a relatively small dataset (1000 elements) to measure performance, which may not accurately represent large-scale usage scenarios.
* The benchmark is run on Chrome 68 and Mac OS X 10.12.6, which may limit its generalizability across different browsers and operating systems.

**Alternatives**

Other alternatives for concatenating arrays in JavaScript include:

* Using `Array.prototype.push()` to concatenate elements directly on the original array.
* Using a loop or `Array.prototype.reduce()` to build up the concatenated array.
* Using other libraries or frameworks that provide optimized array concatenation functions.

Latest run results:

Run details: (Test run date: 6 years ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/68.0.3440.106 Safari/537.36

Browser/OS: Chrome 68 on Mac OS X 10.12.6

View result in a separate tab

Test name	Executions per second
Concat	286440.9 Ops/sec
Concat with spread	38512.0 Ops/sec
ES6 construction with spreads	75675.0 Ops/sec

Related benchmarks:

Javascript concat vs concat with ES6 spread vs ES6 construction with ES6 spread (version: 1)

Comparing performance of: Concat vs Concat with spread vs ES6 construction with spreads

Created: 6 years ago by: Registered User

Jump to the latest result

Concat

Concat with spread

ES6 construction with spreads

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 24 days ago):