Benchmark: Array.prototype.concat vs splice for joining two arrays fixed

Tests:

immutable with concat
var a = [ "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello" ] var b = [ "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello" ] var other = a.concat(b)
direct mutation with splice + spread
var a = [ "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello" ] var b = [ "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello" ] a.splice(-1, 0, ...b);

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
immutable with concat
direct mutation with splice + spread

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 4 years ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/87.0.4280.88 Safari/537.36

Browser/OS: Chrome 87 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
immutable with concat	5977685.0 Ops/sec
direct mutation with splice + spread	3077362.2 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's break down the provided benchmark.

**Benchmark Description**

The benchmark is comparing two approaches to joining two arrays in JavaScript: using `Array.prototype.concat()` and using `splice()` with the spread operator (`...`).

**Options Compared**

The benchmark is testing two options:

1. **Immutable Approach with `concat()`**: This approach creates a new array by concatenating the two input arrays. The original arrays remain unchanged.
2. **Mutable Approach with `splice()` + Spread Operator**: This approach modifies the first array (`.a`) in place by inserting elements from the second array (`b`) at the end of `.a` using `splice()`, and then uses the spread operator to pass the elements of `b` to the `splice()` method.

**Pros and Cons**

1. **Immutable Approach with `concat()`**
	* Pros:
		+ Creates a new array, avoiding mutation of the original arrays.
		+ Can be more predictable and easier to reason about.
	* Cons:
		+ Creates unnecessary memory allocation and copies data.
2. **Mutable Approach with `splice()` + Spread Operator**
	* Pros:
		+ Avoids creating a new array, reducing memory allocation and copying data.
		+ Can be more efficient for large arrays or when the order of elements matters.
	* Cons:
		+ Modifies the original array, which can lead to unexpected behavior if not properly validated.
		+ May have performance overhead due to the `splice()` method.

**Library Used**

None. The benchmark is using built-in JavaScript methods (`Array.prototype.concat()`, `splice()`) without any additional libraries.

**Special JS Feature/Syntax**

The benchmark uses the spread operator (`...`) introduced in ECMAScript 2015 (ES6). This feature allows for more concise and expressive array creation.

**Other Alternatives**

For joining arrays, there are other approaches:

1. **Array.prototype.push()**: Append elements to an existing array using `push()`, followed by assigning the resulting array back to the original variable.
2. **Array.prototype.slice() + Array.prototype.push()**: Create a new array with `slice()` and then append elements using `push()`.
3. **Array.prototype.concat()**: As mentioned earlier, creates a new array by concatenating two input arrays.

Keep in mind that these alternatives may have different trade-offs in terms of performance, memory usage, and predictability compared to the approaches tested in this benchmark.

Related benchmarks:

Array.prototype.concat vs splice for joining two arrays fixed (version: 0)

Comparing performance of: immutable with concat vs direct mutation with splice + spread

Created: 4 years ago by: Guest

Jump to the latest result

immutable with concat

direct mutation with splice + spread

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):