Benchmark: Array isArray vs instanceof vs variable.constructor

Script Preparation code:

var test = [1,2,3,4];
var c;

Tests:

Instanceof
if (test instanceof Array) { c++; }
isArray
if (Array.isArray(test)) { c++; }
variable.constructor
if (test.constructor === Array) { c++; }
variable.constructor name
if (test.constructor.name === 'Array') { c++; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Instanceof
isArray
variable.constructor
variable.constructor name

Fastest: N/A

Slowest: N/A

Latest run results:

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

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/134.0.0.0 Safari/537.36

Browser/OS: Chrome 134 on Windows

View result in a separate tab

Test name	Executions per second
Instanceof	5021448.5 Ops/sec
isArray	5174942.5 Ops/sec
variable.constructor	5276821.5 Ops/sec
variable.constructor name	4160858.5 Ops/sec

Autogenerated LLM Summary (model llama3.2:3b, generated 6 months ago):

LLMs can make mistakes. Check important info.

Let's break down the provided benchmark and explain what's being tested, compared, and the pros/cons of each approach.

**Benchmark Overview**

The website `MeasureThat.net` allows users to create and run JavaScript microbenchmarks. The current benchmark is testing four different approaches to check if a variable is an array:

1. `instanceof Array`
2. `Array.isArray(test)`
3. `test.constructor === Array`
4. `test.constructor.name === 'Array'`

**Approach 1: `instanceof Array`**

This approach uses the `instanceof` operator, which checks if an object is a constructor of another object.

Pros:

* Simple and straightforward
* Works well for most use cases

Cons:

* Can be slower due to the overhead of the `instanceof` operator
* May not work correctly in some cases (e.g., when using `Object.create()` or `Set.prototype.from()`)
* Is specific to JavaScript and may not be portable across other languages

**Approach 2: `Array.isArray(test)`**

This approach uses a built-in method on the `Array` constructor, which checks if an object is an array.

Pros:

* Fast and efficient
* Works well for most use cases
* Portable across other languages (if available)

Cons:

* May not work correctly in some cases (e.g., when using `Object.create()` or `Set.prototype.from()`)
* Is specific to JavaScript

**Approach 3: `test.constructor === Array`**

This approach checks the constructor property of a variable and compares it to the `Array` constructor.

Pros:

* Fast and efficient
* Works well for most use cases

Cons:

* May not work correctly in some cases (e.g., when using `Object.create()` or `Set.prototype.from()`)
* Requires manual construction of the `Array` prototype
* Is specific to JavaScript

**Approach 4: `test.constructor.name === 'Array'`**

This approach uses the `name` property of a constructor to check if it's an array.

Pros:

* Fast and efficient
* Works well for most use cases

Cons:

* Requires modern browsers that support the `name` property (introduced in ECMAScript 2015)
* May not work correctly in older browsers or environments

**Library:**

In this benchmark, no libraries are used. However, if a library were required, some alternatives could be considered:

* Lodash: Provides a `isArray()` function that can be used as an alternative to `Array.isArray()`.
* Jest: Includes an `isArray()` matcher that can be used for similar purposes.

**Special JS Features/Syntax:**

The benchmark does not use any special JavaScript features or syntax, such as async/await, ES6 classes, or TypeScript.

**Other Alternatives:**

If you needed to compare these approaches in a different context, some alternative methods could be considered:

* Use a testing framework like Jest or Mocha, which provide built-in support for comparing function performance.
* Create a custom benchmarking library that provides a similar set of tests and comparisons.
* Use a third-party benchmarking tool, such as WebPageTest or BrowserBench, which can help evaluate the performance of different approaches.

In summary, each approach has its pros and cons, and the choice of method depends on the specific requirements and constraints of your project.

Related benchmarks:

Array isArray vs instanceof vs variable.constructor (version: 1)

Comparing performance of: Instanceof vs isArray vs variable.constructor vs variable.constructor name

Created: 5 years ago by: Registered User

Jump to the latest result

Instanceof

isArray

variable.constructor

variable.constructor name

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 6 months ago):