Benchmark: JS array concatenation

Script Preparation code:

var arr1 = [];
var arr2 = [];

for(var i=1; i<100000; i++) {
 	arr1.push(i); 
}

for(var i=100001; i<200002; i++) {
 	arr2.push(i); 
}

Tests:

concat
const concatenated = arr1.concat(arr2);
push
const concatenated = [...arr1, ...arr2];

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
concat
push

Fastest: N/A

Slowest: N/A

Latest run results:

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

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Let's break down the benchmark and its options.

**Benchmark Definition**

The provided JSON represents a JavaScript microbenchmark that tests two approaches for concatenating arrays: `concat()` and using the spread operator (`...`).

**Options Compared**

1. **`concat()`**: The traditional method of concatenating arrays by calling the `concat()` method on one of the arrays.
2. **Using Spread Operator (`...`)**: A modern approach that uses the spread operator to concatenate arrays.

**Pros and Cons**

* **`concat()`**:
	+ Pros:
		- Widely supported across browsers
		- Easy to understand and implement
	+ Cons:
		- Generally slower than other methods, especially for large arrays
		- Can lead to unnecessary copies of the array being created
* **Using Spread Operator (`...`)**:
	+ Pros:
		- Fastest way to concatenate arrays in modern JavaScript engines
		- Creates a new array with no extra copies or allocations
	+ Cons:
		- Requires support for ES6+ syntax and might not work in older browsers

**Library Used**

None. This benchmark uses built-in JavaScript methods and features.

**Special JS Feature/Syntax**

The `...` spread operator is used to concatenate arrays, which is a relatively new feature introduced in ECMAScript 2015 (ES6).

**Other Alternatives**

Besides the two options compared (`concat()` and using Spread Operator), other approaches for concatenating arrays include:

* Using `Array.prototype.push()`: This method appends elements to the end of an array. It can be used to concatenate arrays, but it's not as efficient as using the spread operator.
* Using `Array.prototype.concat()`: Similar to `push()`, this method returns a new array with all elements from both arrays.

Keep in mind that these alternatives might have different performance characteristics and may not be supported across all browsers or versions of JavaScript.

Related benchmarks:

JS array concatenation (version: 0)

Comparing performance of: concat vs push

Created: 2 years ago by: Guest

Jump to the latest result

concat

push

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

No previous run results

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