Benchmark: Array vs [] post-creation performance

Script Preparation code:

var arr1 = new Array();
var arr2 = [];

Tests:

Array
for(let i = 0; i < 100; i++) arr1[i] = i * 2; for(let i = 0; i < 100; i++) arr1[i] = arr1[i] - 1;
[]
for(let i = 0; i < 100; i++) arr2[i] = i * 2; for(let i = 0; i < 100; i++) arr2[i] = arr2[i] - 1;

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Array
[]

Fastest: N/A

Slowest: N/A

Latest run results:

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

User agent: Mozilla/5.0 (X11; Linux x86_64; rv:109.0) Gecko/20100101 Firefox/110.0

Browser/OS: Firefox 110 on Linux

View result in a separate tab

Test name	Executions per second
Array	2207875.8 Ops/sec
[]	2209144.2 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's dive into explaining the provided benchmark.

**Benchmark Overview**

The test case, named "Array vs [] post-creation performance," is designed to compare the performance of two approaches: using an `Array` object created with the `new` keyword and an empty array literal `[]`. The benchmarks are measuring how long it takes for each approach to execute a series of operations.

**Options Compared**

Two options are being compared:

1. Using an `Array` object created with `new`: `var arr1 = new Array();`
2. Using an empty array literal: `var arr2 = [];`

The main difference between these two approaches is how the array is instantiated and managed. An `Array` object created with `new` requires more memory, as it involves allocating a block of memory for the array's internal buffer. In contrast, an empty array literal `[]` does not require any additional memory allocation.

**Pros and Cons**

**Using an `Array` object created with `new`:**

Pros:

* Explicit memory management: The `new` keyword explicitly allocates memory for the array.
* Better cache locality: The initial allocation of memory can lead to better cache locality, potentially improving performance.

Cons:

* More memory overhead: Creating a new array using `new` requires more memory than creating an empty array literal.
* Slower initialization: The `new` keyword involves additional overhead for creating and initializing the internal buffer.

**Using an empty array literal `[]`:**

Pros:

* Less memory overhead: Creating an empty array literal does not require any additional memory allocation.
* Faster initialization: Array literals are initialized immediately, without the need for a separate allocation step.

Cons:

* Implicit memory management: The array's memory is allocated automatically by JavaScript engines.
* Potential cache locality issues: The implicit allocation may lead to poorer cache locality, potentially affecting performance.

**Other Considerations**

The test also uses `for` loops to iterate over the array elements and perform operations. The loops are initialized with `let i = 0;`, which declares a variable `i` in the scope of each loop iteration.

**Library Usage**

There is no explicit library usage mentioned in this benchmark.

**Special JS Features or Syntax**

There are no special JavaScript features or syntax used in this benchmark. It appears to be a simple, straightforward test case that targets basic array manipulation and performance considerations.

**Alternative Benchmarks**

Other alternatives for measuring array performance might include:

* Comparing the performance of `Array` objects created with different initial capacities.
* Measuring the performance of array methods like `push()`, `splice()`, or `map()`.
* Examining the impact of array lengths on performance in various browsers and environments.

Keep in mind that this specific benchmark only tests the basic allocation overhead of using an `Array` object versus an empty array literal.

Related benchmarks:

Array vs [] post-creation performance (version: 0)

Comparing performance of: Array vs []

Created: one year ago by: Registered User

Jump to the latest result

Array

[]

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

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