Benchmark: myarr unshift vs push + reverse (small array)2

Script Preparation code:

var arr = Array.from({length: 100000}).map((_, i) => ({i}));

Tests:

unshift
var arr2 = []; for (let i = 0; i < arr.length; i++){ arr2.unshift({...arr[i]}); }
reverse
var arr3 = arr.map(o=>({...o})).reverse();

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
unshift
reverse

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: one year ago)

User agent: Mozilla/5.0 (iPhone; CPU iPhone OS 18_2_1 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/18.2 Mobile/15E148 Safari/604.1

Browser/OS: Mobile Safari 18 on iOS 18.2.1

View result in a separate tab

Test name	Executions per second
unshift	0.4 Ops/sec
reverse	260.0 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/cons of each approach.

**Benchmark Overview**

The benchmark is designed to measure the performance difference between two approaches: using `unshift()` and reversing an array by creating a new reversed copy. The test case consists of a small JavaScript array with 100,000 elements, which is first cloned into a new variable `arr2` using `unshift()`. Another test case measures the execution time of reversing the original array `arr` using the `map()` and `reverse()` methods.

**Library Usage**

There is no explicit library usage in this benchmark. However, it's worth noting that the `Array.from()` method used to create the initial array is a part of the ECMAScript standard, which means it's not specific to any particular library or framework.

**Special JavaScript Features/Syntax**

The test cases use the following special features/syntax:

* The spread operator (`{...arr[i]}`) and the `unshift()` method, which are both relatively modern features introduced in ECMAScript 2015 (ES6).
* The `map()` method, which is also a feature introduced in ES6.

**Approach Comparison**

There are two approaches being compared:

1. **Using `unshift()`**: This approach creates a new array and appends the elements to it using `unshift()`, while preserving the original order of elements. The benchmark measures how long this process takes.
2. **Reversing by creating a new reversed copy**: This approach uses the `map()` method to create a new copy of each element in the original array, and then reverses the resulting array using the `reverse()` method. The benchmark measures how long this process takes.

**Pros/Cons of Each Approach**

**Using `unshift()`**:

Pros:

* Preserves the original order of elements
* Can be more efficient if you need to insert elements at a specific position in the array

Cons:

* Creates a new array, which can lead to increased memory usage and garbage collection overhead
* Slower for large arrays due to the need to create a new array and shift elements around

**Reversing by creating a new reversed copy**:

Pros:

* Faster for large arrays since it only requires reversing a single array
* More efficient in terms of memory usage, as no additional arrays are created

Cons:

* Preserves the original order of elements, which might be undesirable in some cases
* Slower when dealing with small arrays due to the overhead of creating multiple copies of elements

**Other Considerations**

When choosing between these approaches, consider the following factors:

* Performance requirements: If you need fast performance for large datasets, reversing by creating a new reversed copy might be the better choice.
* Memory constraints: If memory is limited, using `unshift()` with a large array can lead to increased garbage collection overhead and slower performance.
* Data structure requirements: If preserving the original order of elements is crucial, using `unshift()` might be the better option.

**Alternatives**

Other alternatives to these approaches include:

* Using `splice()` to insert or remove elements from an array
* Using a library like Lodash's `insertAt()`, `map` and `reverse` functions for more complex data manipulation tasks
* Using other libraries or frameworks that provide optimized array manipulation functions, such as React's `useReducer` hook or Vue's `ref` system.

Keep in mind that the best approach will depend on your specific use case and requirements.

Related benchmarks:

myarr unshift vs push + reverse (small array)2 (version: 0)

Comparing performance of: unshift vs reverse

Created: 3 years ago by: Guest

Jump to the latest result

unshift

reverse

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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