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

Script Preparation code:

var arr = [10];

Tests:

unshift
for (let i = 0; i < 100000; i++){ arr.unshift(i); }
push + reverse
for (let i = 0; i < 100000; i++){ arr.push(i); } arr.reverse();

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
unshift
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/123.0.0.0 Safari/537.36

Browser/OS: Chrome 123 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
unshift	0.2 Ops/sec
push + reverse	60.4 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, the different approaches compared, their pros and cons, and other considerations.

**Benchmark Overview**

The benchmark measures the performance of two JavaScript operations on large arrays: `unshift` and `push + reverse`. The test cases create a small initial array with 10 elements and then either use `unshift` to add 100,000 elements from scratch or use `push` followed by `reverse` to add the same amount of elements in reverse order.

**Approaches Compared**

1. **`unshift`**: This operation adds an element to the end of the array without shifting existing elements. It's a relatively simple and efficient operation.
2. **`push + reverse`**: This approach uses `push` to add elements to the end of the array, followed by `reverse` to rearrange the elements in reverse order.

**Pros and Cons**

* **`unshift`**:
	+ Pros: Simple, fast, and efficient ( O(1) average case).
	+ Cons: May not be suitable for arrays with many existing elements, as it can lead to fragmentation.
* **`push + reverse`**:
	+ Pros: Can handle large arrays with many existing elements, as `push` doesn't affect the indexing of existing elements. Also, `reverse` can take advantage of JavaScript's caching mechanisms for reversals.
	+ Cons: More complex and slower than `unshift`, especially for small to medium-sized arrays.

**Other Considerations**

* **Array size**: The benchmark creates a large array with 100,000 elements. This is likely done to minimize the impact of array resizing or reallocation, which can be expensive operations.
* **JavaScript engine**: The benchmark is run on Chrome 123, which may not be the most recent version. Additionally, the `RawUAString` field suggests that the browser's User Agent string is generated by a custom test harness.
* **Device and OS**: The benchmark is run on a desktop with Mac OS X 10.15.7.

**Library/Dependencies**

None of the provided code snippets use any external libraries or dependencies, other than the built-in JavaScript `Array` methods.

**Special JS Features/Syntax**

There are no special JavaScript features or syntax used in this benchmark beyond the standard array operations and conditional statements (e.g., `for`, `let`, `const`).

Related benchmarks:

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

Comparing performance of: unshift vs push + reverse

Created: 3 years ago by: Guest

Jump to the latest result

unshift

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):