Benchmark: arr unshift vs reverse + push + reverse (small array)

Script Preparation code:

var arr = [10];

Tests:

unshift
for (let i = 0; i < 10; i++){ arr.unshift(i); }
reverse + push + reverse
for (let i = 0; i < 10; i++){ arr.reverse(); arr.push(i); arr.reverse(); }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
unshift
reverse + push + reverse

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 2 years ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/119.0.0.0 Safari/537.36

Browser/OS: Chrome 119 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
unshift	1436.5 Ops/sec
reverse + push + reverse	65.4 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 benchmark and explain what's being tested, compared, and the pros and cons of each approach.

**Benchmark Overview**

The test measures the performance difference between two methods for inserting an element at the beginning of an array: `unshift()` and a custom approach using `reverse()`, followed by `push()`, and then another `reverse()`.

**Script Preparation Code**
```javascript
var arr = [10];
```
This code initializes an empty array with one element, which will be used as the test subject for both benchmarks.

**Html Preparation Code**

There is no HTML preparation code provided, so we can assume that the benchmark is running in a pure JavaScript environment.

**Benchmark Definitions**

We have two individual test cases:

1. **`unshift`**: This benchmark measures the performance of using `unshift()` to insert elements at the beginning of the array.
```javascript
for (let i = 0; i < 10; i++) {
  arr.unshift(i);
}
```
2. **`reverse + push + reverse`**: This benchmark measures the performance of a custom approach that first reverses the array, pushes an element onto it, and then reverses the array again.
```javascript
for (let i = 0; i < 10; i++) {
  arr.reverse();
  arr.push(i);
  arr.reverse();
}
```
**Comparison**

The benchmark compares the performance of these two approaches:

* `unshift()`: Directly inserting an element at the beginning of the array.
* `reverse + push + reverse`: A custom approach that first reverses the array, pushes an element onto it, and then reverses the array again.

**Pros and Cons**

1. **`unshift()`**:
	* Pros: Efficient and straightforward approach, minimizing additional array modifications.
	* Cons: Can be slower than other approaches if the resulting array is much larger than the original one due to insertion overhead.
2. **`reverse + push + reverse`**:
	* Pros: May perform better when the resulting array size is large, as it only modifies the existing array structure once.
	* Cons: Requires additional operations (reversing and pushing) that can lead to slower performance compared to a single `unshift()` call.

Other alternatives might include:

1. **`splice()`**: Inserting an element at a specific position in the array using `splice()`.
```javascript
for (let i = 0; i < 10; i++) {
  arr.splice(0, 0, i);
}
```
2. **Custom implementation using indexing**: Directly accessing and modifying the underlying array buffer.
```javascript
for (let i = 0; i < 10; i++) {
  var buffer = new ArrayBuffer(arr.length * 4); // assuming 32-bit integers
  var view = new Uint32Array(buffer);
  arr[0] = i;
}
```
Keep in mind that these alternatives might not be as efficient or straightforward as the `unshift()` approach.

**Libraries and Special Features**

There are no libraries mentioned in this benchmark. However, if you were to use a library like Lodash or Ramda, it's possible that one of their utility functions (e.g., `lodash.array.unshift()`) would be used instead of vanilla JavaScript's `unshift()` method.

Special JS features like async/await, promise-based APIs, or modern syntax like arrow functions and classes are not mentioned in this benchmark.

Related benchmarks:

arr unshift vs reverse + push + reverse (small array) (version: 0)

Comparing performance of: unshift vs reverse + push + reverse

Created: 2 years ago by: Registered User

Jump to the latest result

unshift

reverse + push + reverse

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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