Benchmark: instanceof vs constructor.name vs field

Script Preparation code:

var A = class A {
	_className = 'A'
}

var a = new A()

Tests:

instanceof
var b = a instanceof A
constructor.name
var b = a.constructor.name === 'A'
field
var b = a._className === 'A'

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
instanceof
constructor.name
field

Fastest: N/A

Slowest: N/A

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

LLMs can make mistakes. Check important info.

Let's break down the provided JSON and explain what's being tested, compared, and their pros/cons.

**Benchmark Definition**

The benchmark definition is a JSON object that contains three test cases:

1. `instanceof`
2. `constructor.name`
3. `field`

Each test case represents a different way to check if an instance of a class `A` is valid.

**What's being tested?**

In this benchmark, we're testing the performance difference between three ways to check if an object `a` is an instance of class `A`, which has a private property `_className` set to `'A'`.

The test cases are:

1. `instanceof A`: checks if `a` is an instance of class `A`.
2. `constructor.name === 'A'`: checks the name of the constructor function of `a`. Since `a` is created using the class syntax, its constructor function has the same name as the class.
3. `_className === 'A'`: directly accesses the private property `_className` of class `A`.

**Options compared**

The benchmark compares the performance difference between these three approaches:

1. Using the `instanceof` operator (`a instanceof A`)
2. Accessing the constructor name using the `constructor.name` property (`a.constructor.name === 'A'`)
3. Directly accessing a private property (`_className === 'A'`)

**Pros and Cons**

Here's a brief summary of each approach:

1. **Using `instanceof`**:
	* Pros: Simple, easy to read, and maintain.
	* Cons: May have performance overhead due to the need for a runtime check.
2. **Accessing `constructor.name`**:
	* Pros: Fast, as it only requires a single property access.
	* Cons: May not work correctly if the class has multiple constructors or if the constructor name is changed at runtime.
3. **Directly accessing `_className`**:
	* Pros: Fast and direct, as it only accesses a private property.
	* Cons: May break if the private property is renamed, deleted, or modified in an unexpected way.

**Library**

There's no explicit library mentioned in the benchmark definition or test cases. However, class syntax and private properties are part of the JavaScript language.

**Special JS feature or syntax**

The `class` keyword and private properties (`_className`) were introduced in ECMAScript 2015 (ES6). The `instanceof` operator has been a part of JavaScript since its inception.

Overall, this benchmark is testing the performance trade-offs between three different approaches to check if an object is an instance of a class. The results can help developers understand which approach to use depending on their specific use case and performance requirements.

Latest run results:

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

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36

Browser/OS: Chrome 120 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
instanceof	15258774.0 Ops/sec
constructor.name	21992666.0 Ops/sec
field	28818622.0 Ops/sec

Related benchmarks:

instanceof vs constructor.name vs field (version: 0)

Comparing performance of: instanceof vs constructor.name vs field

Created: one year ago by: Registered User

Jump to the latest result

instanceof

constructor.name

field

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):