Benchmark: Array initialization: preallocate vs push with objects

Tests:

Preallocate
var N = 10000; var result = new Array(N); for (var i = 0; i < N; i++) { result[i] = {n: N}; }
Push
var N = 10000; var result = []; for (var i = 0; i < N; i++) { result.push({n: N}); }

Historical Performance Data aggregated from 31 community runs

Desktop Results:

Chrome 21 runs

Preallocate

46K/s

Push

30K/s

Fastest: Preallocate (1.6x faster)

View exact numbers

✓ Preallocate: 46,320 ops/sec
• Push: 29,783 ops/sec

Firefox 10 runs

Preallocate

11K/s

Push

11K/s

View exact numbers

✓ Preallocate: 11,059 ops/sec
• Push: 10,609 ops/sec

Results show median performance across all community submissions. Run this benchmark yourself to verify on your device.

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Preallocate
Push

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 2 months ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/148.0.0.0 Safari/537.36 Edg/148.0.0.0

Browser/OS: Chrome 148 on Windows

View result in a separate tab

Preallocate

17K/s

Push

9K/s

View exact numbers

Test name	Executions per second
✓ Preallocate	17,443 Ops/sec
Push	9,343 Ops/sec

Autogenerated LLM Summary (model gpt-4o-mini, generated one year ago):

LLMs can make mistakes. Check important info.

The benchmark you provided evaluates two different methods of initializing and populating an array in JavaScript: "Preallocate" and "Push".

### Approach Comparison

1. **Preallocate Method**
   - **Code**:
     ```javascript
     var N = 10000;
     var result = new Array(N);
     for (var i = 0; i < N; i++) {
       result[i] = {n: N};
     }
     ```
   - **Description**: This method preallocates memory for an array with a set size (N). The array is created with `new Array(N)`, which reserves space for 10,000 elements upfront. Then, the loop fills the array with objects.

- **Pros**:
     - **Memory Allocation**: Allocating memory in one step can be more efficient because it minimizes the number of memory re-allocations needed when the array grows.
     - **Initial Setup**: Faster when the number of items being added is known beforehand as it doesn't involve the overhead of dynamic resizing.

- **Cons**:
     - If more elements are added beyond the preallocated size, it requires reallocation.
     - Initializing an unused array could consume memory unnecessarily if the pre-allocation isn't fully utilized.

2. **Push Method**
   - **Code**:
     ```javascript
     var N = 10000;
     var result = [];
     for (var i = 0; i < N; i++) {
       result.push({n: N});
     }
     ```
   - **Description**: This method starts with an empty array and uses the `push()` method to add 10,000 objects to it during the loop.

- **Pros**:
     - **Dynamic Sizing**: It allows for a dynamically sized array which can accommodate an uncertain number of elements.
     - **Simplicity**: It is easy to understand and straightforward, particularly when the final size of the array is not known.

- **Cons**:
     - Memory reallocation might occur as the array grows, which can lead to performance penalties, especially if the elements exceed the initially allocated space.

### Benchmark Results

From the provided benchmark results:
- **Preallocate** achieved **15,464.01 executions per second**.
- **Push** achieved **14,628.36 executions per second**.

### Considerations

The benchmark indicates that the "Preallocate" method outperformed the "Push" method in this specific test case. However, the actual performance can vary depending on factors like the JavaScript engine optimization, the execution environment, and how the benchmarks are run (e.g., browser version, or device used).

### Alternative Techniques

Other alternatives to consider for array initialization and population include:

- **Using Typed Arrays**: For performance-critical applications, such as numerical computations, Typed Arrays provide an alternative that utilizes a contiguous block of memory and can offer better performance with numerical data. Examples include `Int32Array`, `Float64Array`, etc.
  
- **Using Array.from**: This method allows for array creation based on array-like structures or iterable objects. This can be useful for creating arrays from existing collections efficiently.

- **Spread Operator**: The spread operator (`...`) can be used in newer JavaScript to expand iterable structures into array literals, which might be more readable in some scenarios.

In summary, choosing between these approaches depends on the specific requirements of your application, such as performance needs, memory considerations, and coding style preferences.

Array initialization: preallocate vs push with objects (version: 1)

Comparing performance of: `Preallocate vs Push`

Created: one year ago by: Guest

Go to the latest result

Preallocate

Push

Historical Performance Data aggregated from 31 community runs

Desktop Results:

Chrome 21 runs

Firefox 10 runs

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model gpt-4o-mini, generated one year ago):

Array initialization: preallocate vs push with objects (version: 1)

Comparing performance of: Preallocate vs Push

Created: one year ago by: Guest

Go to the latest result

Preallocate

Push

Historical Performance Data aggregated from 31 community runs

Desktop Results:

Chrome 21 runs

Firefox 10 runs

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model gpt-4o-mini, generated one year ago):

Related benchmarks

Comparing performance of: `Preallocate vs Push`