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

Script Preparation code:

var arr = [];

Tests:

unshift
for (let i = 0; i < 50; i++){ arr.unshift(i); }
push + reverse
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: 9 months ago)

User agent: Mozilla/5.0 (X11; Linux x86_64; rv:140.0) Gecko/20100101 Firefox/140.0

Browser/OS: Firefox 140 on Linux

View result in a separate tab

Test name	Executions per second
unshift	10909.1 Ops/sec
push + reverse	101.5 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.

**Benchmark Overview**

The benchmark compares two approaches to add elements to an array: `arr.unshift(i)` and `arr.push(i) + arr.reverse()`. The test case creates an empty array, fills it with 50 elements using one of these methods, and then measures the execution time.

**Options Compared**

There are two options being compared:

1. **unshift**: This method adds a new element to the beginning of the array.
2. **push + reverse**: This approach first adds a new element to the end of the array using `arr.push(i)`, and then reverses the entire array using `arr.reverse()`.

**Pros and Cons**

* **Unshift**:
	+ Pros: Efficient for adding elements to the beginning of the array, as it only requires updating the index of each element.
	+ Cons: Can be slower than `push` because it involves updating an internal array structure, which can lead to cache misses.
* **Push + reverse**:
	+ Pros: Can be faster than `unshift` because reversing the entire array at once can reduce cache locality issues. However, this approach is less efficient for small arrays or frequent insertions.
	+ Cons: Requires two operations (push and reverse), which can increase overall execution time.

**Library**

The benchmark does not use any external libraries beyond what's built into JavaScript (e.g., `Array.prototype.unshift`, `Array.prototype.push`, `Array.prototype.reverse`).

**Special JS Feature or Syntax**

There is no special JS feature or syntax being tested in this benchmark. The focus is on the performance comparison between two common array manipulation methods.

**Other Considerations**

* The benchmark creates a new array of size 50 for each test case, which can impact execution time.
* The `unshift` method may perform better if the array grows quickly because it only requires updating indices, while `push + reverse` involves reversing the entire array.
* In real-world scenarios, you might not create an empty array and fill it with elements in a single loop. This benchmark simplifies the test case to focus solely on the performance comparison.

**Other Alternatives**

If you're interested in exploring other approaches or variations, consider these alternatives:

1. **Array.prototype.splice**: Instead of `unshift` and `push`, use `splice` to remove and add elements from the array.
2. **Array.prototype.concat**: Compare the performance of concatenating multiple arrays using `concat` versus creating a new array with `push`.
3. **For-loops vs Array methods**: Compare the performance of using traditional for-loops (e.g., `for (var i = 0; i < 50; ++i) { arr[i] = i; }`) versus using built-in array methods like `forEach`, `map`, or `reduce`.
4. **Array initialization vs allocation**: Investigate how the performance of initializing an array with a fixed size (`arr = new Array(50);`) compares to dynamically allocating memory using `new Int32Array()` or other native array types.

Keep in mind that these alternative benchmarks will likely have different test cases and focus on specific aspects of JavaScript performance.

Related benchmarks:

arr unshift vs push + reverse (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):