Benchmark: arr unshift vs push + reverse (recreating size 50 array)

Tests:

unshift
var arr = []; for (let i = 0; i < 50; i++){ arr.unshift(i); }
push + reverse
var arr = []; for (let i = 0; i < 50; 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 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36

Browser/OS: Chrome 120 on Windows

View result in a separate tab

Test name	Executions per second
unshift	923963.8 Ops/sec
push + reverse	10526558.0 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's dive into the explanation of the MeasureThat.net benchmark.

**Benchmark Overview**

The benchmark measures the performance difference between two approaches: using `arr.unshift()` to add elements to an array, versus using `push()` followed by reversing the array.

**Options Compared**

There are only two options being compared in this benchmark:

1. **`unshift()`**: adds elements to the beginning of the array.
2. **`push()` + `reverse()`**: adds elements to the end of the array and then reverses it.

**Pros and Cons of Each Approach**

* **`unshift()`**:
	+ Pros: can be faster for certain scenarios (e.g., when adding elements at the beginning of an array), as it avoids the overhead of reversing the array.
	+ Cons: can be slower than `push()` + `reverse()` in general, since it requires shifting all existing elements to make space at the beginning of the array.
* **`push()` + `reverse()`**:
	+ Pros: is generally faster and more memory-efficient, as it adds elements to the end of the array without requiring any shifts or reversals.
	+ Cons: requires two operations (adding elements and reversing), which can be slower than a single operation like `unshift()`, especially for small arrays.

**Library**

There is no explicit library mentioned in the benchmark definition. However, it's likely that the standard JavaScript built-in methods (`arr.unshift()` and `arr.push()`) are being used.

**Special JS Features or Syntax**

There are no special features or syntax explicitly mentioned in this benchmark. The code snippets provided only use basic JavaScript constructs like loops, arrays, and function declarations.

**Other Alternatives**

For comparison, other approaches to adding elements to an array could include:

* Using `splice()` instead of `push()`: `arr.splice(0, 0, i);`
* Using a custom implementation using indexed assignment: `arr[i] = i;` (not shown in the benchmark)
* Using a library or framework-specific method (if applicable)

Keep in mind that the performance differences between these alternatives may vary depending on the specific use case and requirements.

Overall, this benchmark provides a simple yet insightful comparison of two common approaches to adding elements to an array in JavaScript.

Related benchmarks:

arr unshift vs push + reverse (recreating size 50 array) (version: 0)

Comparing performance of: unshift vs push + reverse

Created: 2 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):