Benchmark: Array initialization: preallocate vs push

Tests:

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

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: 4 months ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:146.0) Gecko/20100101 Firefox/146.0

Browser/OS: Firefox 146 on Windows

View result in a separate tab

Test name	Executions per second
Preallocate	18513.1 Ops/sec
Push	17527.0 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 benchmark and its components.

**Benchmark Definition**

The provided JSON defines two benchmark cases:

1. **Preallocate**: This test case measures the performance of creating an array using the `new Array()` constructor and then populating it with 10,000 elements by assigning a value to each element.
2. **Push**: This test case measures the performance of creating an empty array and then populating it with 10,000 elements using the `push()` method.

**Options Compared**

The two benchmark cases compare the performance of two approaches:

1. **Preallocation**: Creating an array using the `new Array()` constructor and immediately populating it.
2. **Push**: Creating an empty array and then pushing elements onto it using the `push()` method.

**Pros and Cons**

**Preallocation (New Array())**

Pros:

* Can be faster because the array is created in a single step, reducing overhead.
* Can lead to better memory locality, as all elements are initialized at once.

Cons:

* May require more memory upfront, depending on the size of the array.
* Can be slower if the array is very large, due to the initial creation cost.

**Push (Array.push())**

Pros:

* Requires less memory upfront, as only a single element needs to be allocated initially.
* Can be faster for large arrays, since pushing elements one by one reduces overhead.

Cons:

* May lead to poorer memory locality, as each push operation creates a new allocation.
* Can result in slower performance due to the repeated allocation and deallocation of memory.

**Library**

None of the benchmark cases use any libraries. The tests are self-contained JavaScript code that creates arrays and performs operations on them.

**Special JS Feature/Syntax**

There is no special JavaScript feature or syntax used in these benchmark cases. They use standard JavaScript syntax for creating arrays, loops, and push operations.

**Other Alternatives**

To measure the performance of array initialization, you could also consider other approaches, such as:

* Using a library like `lodash` or `ramda`, which provide optimized array creation methods.
* Implementing a custom array allocation function using native code (e.g., C++).
* Measuring the performance of different data structures, such as arrays, linked lists, or vectors.

In summary, this benchmark compares two common approaches to initializing and populating arrays in JavaScript: preallocation using `new Array()` and pushing elements onto an empty array using `push()`. The choice between these approaches depends on the specific use case and performance requirements.

Related benchmarks:

Array initialization: preallocate vs push (version: 0)

Comparing performance of: Preallocate vs Push

Created: 7 years ago by: Guest

Jump to the latest result

Preallocate

Push

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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