Benchmark: replace an array in JavaScript - splice vs push vs for

Script Preparation code:

var size = 10000;
var arr1 = [];
var arr2 = [];
for (var i = 0; i < size; i++) {
  arr1.push(i);
  arr2.push(i);
}

Tests:

push
arr2.length = 0; arr2.push(...arr1);
splice
arr2.splice(0, arr2.length, ...arr1);
for
if (arr2.length !== arr1.length) arr2.length = arr1.length; for (let i = 0, length = arr1.length; i < length; ++i) { arr2[i] = arr1[i]; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
push
splice
for

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 5 months ago)

User agent: Mozilla/5.0 (X11; Linux x86_64; rv:145.0) Gecko/20100101 Firefox/145.0

Browser/OS: Firefox 145 on Linux

View result in a separate tab

Test name	Executions per second
push	42226.1 Ops/sec
splice	4628.0 Ops/sec
for	82308.8 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 benchmark and explain what is being tested.

**Benchmark Overview**

The benchmark tests three different approaches to replace an array in JavaScript:

1. Using `push()` method
2. Using `splice()` method
3. Using a manual loop (for)

**Library Used**

There is no specific library used in this benchmark, only built-in JavaScript functions and operators.

**Special JS Feature/Syntax**

None mentioned explicitly, but note that the use of `let` keyword for variable declaration (`"for": { ... "for": { let i = 0; ... } }`) suggests a recent JavaScript feature introduced with ECMAScript 2015 (ES6). However, since this benchmark is not specifically testing this feature, we'll ignore it.

**Benchmark Test Cases**

The benchmark consists of three test cases:

1. **Push**: The first test case creates two arrays `arr1` and `arr2`, populates them with numbers from 0 to 9999 (10000 iterations), and then uses the `push()` method to add all elements of `arr1` to `arr2`. The goal is to see which approach takes less time.
2. **Splice**: The second test case creates two arrays `arr1` and `arr2`, populates them with numbers from 0 to 9999 (10000 iterations), and then uses the `splice()` method to replace all elements of `arr2` with those of `arr1`. The goal is to see which approach takes less time.
3. **For**: The third test case creates two arrays `arr1` and `arr2`, populates them with numbers from 0 to 9999 (10000 iterations), and then uses a manual loop to assign elements from `arr1` to `arr2`. The goal is to see which approach takes less time.

**Options Compared**

The benchmark compares the performance of three different approaches:

* **Push**: Using the `push()` method to add elements to an array.
* **Splice**: Using the `splice()` method to replace elements in an array.
* **For**: Using a manual loop to assign elements from one array to another.

**Pros and Cons**

Here are some pros and cons of each approach:

* **Push**:
	+ Pros: Simple, efficient, and widely supported. It uses the least amount of memory (no need to create a new array).
	+ Cons: May not be suitable for large arrays or arrays with many duplicates.
* **Splice**:
	+ Pros: Allows for more control over the replacement process. Can be used for both inserting and removing elements.
	+ Cons: Uses more memory than `push()` since it needs to create a new array. Also, can be slower due to the overhead of creating and manipulating arrays.
* **For**:
	+ Pros: Provides fine-grained control over the assignment process. Suitable for large arrays or arrays with many duplicates.
	+ Cons: Can be slow due to the overhead of the loop. Requires manual memory management.

**Other Alternatives**

There are other alternatives that could be used to replace an array in JavaScript, such as:

* Using `concat()`: Concatenating two arrays using the `concat()` method.
* Using `set()`: Using the `Set` data structure to store unique elements from one array and then converting it back to an array using `Array.from()`.
* Using `reduce()`: Using the `reduce()` method to combine elements from two arrays into a single array.

However, these alternatives may have different performance characteristics or trade-offs compared to the approaches tested in this benchmark.

Related benchmarks:

replace an array in JavaScript - splice vs push vs for (version: 0)

Based on question on http://stackoverflow.com/questions/1232040/how-do-i-empty-an-array-in-javascript

Comparing performance of: push vs splice vs for

Created: 3 years ago by: Guest

Jump to the latest result

push

splice

for

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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