Benchmark: instanceof vs in

Script Preparation code:

class ClassFoo {
    constructor() {
        this.bar = 1;
    }
}

var Foo = ClassFoo;
var foo = new Foo();

Tests:

instanceof test
foo instanceof Foo
in test
'bar' in foo

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
instanceof test
in test

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 6 months ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:144.0) Gecko/20100101 Firefox/144.0

Browser/OS: Firefox 144 on Windows

View result in a separate tab

Test name	Executions per second
instanceof test	352450752.0 Ops/sec
in test	3898128896.0 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's break down the provided JSON benchmark definition and explanation what is being tested.

**Benchmark Definition**

The benchmark consists of two test cases:

1. `foo instanceof Foo`
2. `'bar' in foo`

**What is being tested?**

These two test cases are comparing the performance of the JavaScript operators `instanceof` and `in`. The `instanceof` operator checks if an object is an instance of a specific constructor, whereas the `in` operator checks if a property (in this case, `bar`) is present in an object.

**Options compared**

The two options being compared are:

1. `foo instanceof Foo`: This uses the `instanceof` operator to check if `foo` is an instance of the `Foo` class.
2. `'bar' in foo`: This uses the `in` operator to check if `bar` is a property present in the `foo` object.

**Pros and Cons**

* **instanceof**: This method can be more accurate for checking if an object is an instance of a specific class, as it takes into account the constructor's prototype chain. However, it may also lead to slower performance due to its use of dynamic typing.
* **in**: This method is generally faster than `instanceof` because it uses a simpler property lookup operation. However, it can return false positives if the object has inherited properties from other classes.

**Other considerations**

In this specific benchmark, the `foo instanceof Foo` test case may be affected by the fact that `Foo` is defined using the `class` keyword, which creates a new scope for the constructor. This could lead to a slight overhead in terms of performance.

**Library and special features**

There is no library being used in this benchmark. However, it does utilize some JavaScript features:

* **`class` keyword**: This feature allows defining classes with constructors.
* **Arrow functions**: Although not explicitly shown, arrow functions are implied by the use of `var foo = new Foo();`.

**Alternatives**

If you wanted to write a similar benchmark for these two operators, you could consider using other languages or frameworks that also support operator overloading, such as:

* Python: Using `isinstance()` and `in`
* Java: Using `instanceof` and `containsKey()`
* C++: Using `dynamic_cast` and `std::map::find`

However, keep in mind that each language has its own strengths and weaknesses when it comes to performance, and the results may vary depending on the specific implementation and hardware.

Related benchmarks:

instanceof vs in (version: 0)

Comparing performance of: instanceof test vs in test

Created: 2 years ago by: Guest

Jump to the latest result

instanceof test

in test

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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