Benchmark: Array.isArray vs Object.prototype.toString vs [].constructor vs instanceof

Tests:

Array.isArray
Array.isArray([])
instanceof
[] instanceof Array
[].constructor
[].constructor === Array
Object.prototype.toString
Object.prototype.toString.call([]) === '[object Array]'

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Array.isArray
instanceof
[].constructor
Object.prototype.toString

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 25 days ago):

LLMs can make mistakes. Check important info.

Let's break down what's being tested in the provided JSON.

**Benchmark Overview**

The benchmark is designed to compare four different approaches for checking if an object is an array:

1. `Array.isArray()`
2. `instanceof Array`
3. `[].constructor === Array`
4. `Object.prototype.toString.call([]) === '[object Array]'`

These methods are compared in the context of creating and manipulating empty arrays.

**Options Comparison**

Here's a brief overview of each option, their pros and cons:

1. **`Array.isArray()`**: This is a built-in JavaScript function that returns `true` if the object passed to it is an array-like object (including arrays). Pros: simple, concise, and widely supported. Cons: may return incorrect results for non-array-like objects.
2. **`instanceof Array`**: This method checks if an object is an instance of the `Array` constructor. Pros: accurate for most cases, but it only works with constructors that have a built-in `prototype` property. Cons: may not work as expected with certain types of objects (e.g., functions or non-constructor objects).
3. **`[].constructor === Array`**: This approach checks if the constructor property of an array is equal to the `Array` constructor. Pros: accurate and type-safe, but it requires knowledge of constructors and may be less readable than other options. Cons: less common use cases.
4. **`Object.prototype.toString.call([]) === '[object Array]'`**: This method uses a helper function (`toString`) from `Object.prototype` to check if the result is an array representation. Pros: accurate, but it relies on internal implementation details of `Object.prototype.toString`. Cons: may break with changes to JavaScript engines or implementations.

**Library and Special JS Features**

None of the test cases use external libraries or special JavaScript features beyond what's required for basic syntax checking.

**Other Alternatives**

Other methods for checking if an object is an array might include:

* Using `Array.prototype.forEach()` (not tested in this benchmark)
* Implementing a custom "is-array" function using bitwise operations
* Using a third-party library like Lodash

Keep in mind that the specific use cases and requirements may affect the choice of alternative methods.

Let me know if you have any further questions!

Latest run results:

Run details: (Test run date: 8 months ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/122.0.0.0 Safari/537.36

Browser/OS: Chrome 122 on Windows

View result in a separate tab

Test name	Executions per second
Array.isArray	6689298.0 Ops/sec
instanceof	6722487.5 Ops/sec
[].constructor	7276046.0 Ops/sec
Object.prototype.toString	6339130.5 Ops/sec

Related benchmarks:

Array.isArray vs Object.prototype.toString vs [].constructor vs instanceof (version: 0)

Array.isArray vs Object.prototype.toString vs [].constructor vs instanceof

Comparing performance of: Array.isArray vs instanceof vs [].constructor vs Object.prototype.toString

Created: 8 months ago by: Guest

Jump to the latest result

Array.isArray

instanceof

[].constructor

Object.prototype.toString

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 25 days ago):