Benchmark: arr unshift vs push + reverse (size 20 array)

Script Preparation code:

var arr = [];

Tests:

unshift
for (let i = 0; i < 200; i++){ arr.unshift(i); }
push + reverse
for (let i = 0; i < 200; 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: 11 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	2146.5 Ops/sec
push + reverse	90.5 Ops/sec

Autogenerated LLM Summary (model gpt-4o-mini, generated 11 months ago):

LLMs can make mistakes. Check important info.

The benchmark defined in the provided JSON tests the performance of two different methods for adding elements to an array in JavaScript: **`unshift`** and a combination of **`push`** followed by **`reverse`**. This gives insight into which approach is more efficient when constructing an array.

### Test Cases Overview

1. **Test Case: `unshift`**
   - **Description**: This method adds elements to the beginning of the array. The benchmark runs a loop that continuously adds the integers from `0` to `199` to the front of the array using `arr.unshift(i);`.
   - **Performance Result**: This approach achieved approximately **2146.54 executions per second**.

2. **Test Case: `push + reverse`**
   - **Description**: This method involves adding the same integers using `arr.push(i);`, which appends each element to the end of the array, followed by reversing the array with `arr.reverse();` to achieve a similar final structure as the first method.
   - **Performance Result**: This approach yielded about **90.52 executions per second**.

### Pros and Cons of the Approaches

**`unshift`:**
- **Pros**:
  - Simplicity: The operation is straightforward—elements are added directly to the front.
- **Cons**:
  - Performance: As the array grows, `unshift` becomes slower because it needs to shift all existing elements to accommodate the new element at index `0`. This leads to a time complexity of O(n) per insertion.

**`push + reverse`:**
- **Pros**:
  - Batch Processing: Elements are added in one go to the end, where `push` is typically optimized for performance, making it effectively O(1) per insertion.
  - Less shifting of elements compared to `unshift`.
- **Cons**:
  - Additional Memory Usage: This approach requires extra memory for the `reverse` operation, as it doesn't modify the array in place, but rather creates a new order.
  - Complexity: Involves two operations (pushing and reversing), which could be seen as less straightforward.

### Other Considerations

- **Usability**: Depending on the specific requirements of an application, one approach may be preferred over the other. If the order of elements is critical and needs to be at the front frequently, `unshift` might be the choice despite its performance drawbacks.
- **Scaling**: For large datasets and frequent insertions, the performance costs of `unshift` can become a significant bottleneck, making `push` + `reverse` a better alternative when the final order is not a concern during data accumulation.
  
### Alternative Approaches

- **Using `concat` and Array Spread**: For scenarios where multiple values are being added, using `Array.concat()` or the spread operator (`...`) can be more efficient and more readable.
- **Chunking with `splice`**: In scenarios where the array needs to be built from both ends or inserted in various positions, `splice` may offer additional flexibility, albeit at a similar performance cost to `unshift`.
- **Using Data Structures Like Linked Lists**: If frequent insertions and deletions are necessary, a different data structure like a linked list might outperform array approaches in terms of scalability and performance.

In summary, this benchmark effectively highlights the performance trade-offs between direct and batch array manipulation methods in JavaScript, beneficial for developers making decisions based on array performance in their applications.

Related benchmarks:

arr unshift vs push + reverse (size 20 array) (version: 1)

Comparing performance of: unshift vs push + reverse

Created: 11 months 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 gpt-4o-mini, generated 11 months ago):