Benchmark: Array initialization

Script Preparation code:

var len = 100;

Tests:

Decide length in `new`
var a = new Array(len), i; for (i = 0; i < len; i++) { a[i] = i; } window.a = a;
Decide length with .length
var a = [], i; a.length = len; for (i = 0; i < len; i++) { a[i] = i; } window.a = a;
Push items separately
var a = [], i; for (i = 0; i < len; i++) { a.push(i); } window.a = a;
Assign items separately
var a = [], i; for (i = 0; i < len; i++) { a[i] = i; } window.a = a;

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Decide length in `new`
Decide length with .length
Push items separately
Assign items separately

Fastest: N/A

Slowest: N/A

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

LLMs can make mistakes. Check important info.

Measuring JavaScript performance is crucial for optimizing web applications. Let's dive into the provided benchmark and explain what's being tested, the options compared, pros and cons of each approach, library usage, special features or syntax, and alternative approaches.

**Benchmark Overview**

The benchmark compares four different ways to initialize an array in JavaScript:

1. **`new` keyword with length**: `var a = new Array(len), i; for (i = 0; i < len; i++) { ta[i] = i; } window.a = a;`
2. **Length assignment**: `var a = [], i; a.length = len; for (i = 0; i < len; i++) { ta[i] = i; } window.a = a;`
3. **Push items separately**: `var a = [], i; for (i = 0; i < len; i++) { ta.push(i); } window.a = a;`
4. **Assign items separately**: `var a = [], i; for (i = 0; i < len; i++) { ta[i] = i; } window.a = a;`

**Options Compared**

The benchmark compares the performance of these four approaches:

* **`new` keyword with length**: This method creates an array using the `new` keyword and specifies the initial length. The length is then assigned to the array.
* **Length assignment**: In this approach, an empty array is created, and its length is set to the desired value. Then, elements are pushed onto the array using a loop.
* **Push items separately**: This method creates an empty array and pushes individual elements into it using `ta.push(i)`.
* **Assign items separately**: Similar to the previous approach, but elements are assigned directly to the array using `ta[i] = i`.

**Pros and Cons of Each Approach**

1. **`new` keyword with length**:
	* Pros: Creates an array with a fixed length, which can be more memory-efficient.
	* Cons: Requires specifying the initial length, which might lead to errors if not done correctly.
2. **Length assignment**:
	* Pros: More flexible than using `new`, as the length is set before pushing elements.
	* Cons: Creating an empty array first and then pushing elements can be less efficient.
3. **Push items separately**:
	* Pros: Pushing elements onto the array one by one can lead to better performance, especially for large arrays.
	* Cons: Requires using `push()`, which might not be as readable or intuitive as other approaches.
4. **Assign items separately**:
	* Pros: More concise and readable than pushing individual elements onto the array.
	* Cons: Might lead to slower performance due to the overhead of assigning each element individually.

**Library Usage**

None of the benchmark test cases use any external libraries or dependencies beyond the built-in JavaScript functions (`Array`, `push()`, etc.).

**Special Features or Syntax**

There are no special features or syntax used in these benchmark test cases. They are all standard JavaScript approaches.

**Alternative Approaches**

Other ways to initialize an array in JavaScript include:

* Using `Array.from()` with an initial value: `var a = Array(len).fill(i);`
* Using `Array.prototype.fill()` method: `var a = new Array(len).fill(i);`
* Using `Map` or `Set` data structures, which provide more efficient ways to create arrays of unique values.

Keep in mind that the performance differences between these approaches may vary depending on the specific use case and browser implementation.

Latest run results:

Run details: (Test run date: 7 years ago)

User agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/55.0.2883.87 Safari/537.36

Browser/OS: Chrome 55 on Windows 7

View result in a separate tab

Test name	Executions per second
Decide length in `new`	79507.8 Ops/sec
Decide length with .length	78777.3 Ops/sec
Push items separately	70483.2 Ops/sec
Assign items separately	70598.0 Ops/sec

Related benchmarks:

Array initialization (version: 4)

Comparing performance of: Decide length in `new` vs Decide length with .length vs Push items separately vs Assign items separately

Created: 7 years ago by: Registered User

Jump to the latest result

Decide length in `new`

Decide length with .length

Push items separately

Assign items separately

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):