Benchmark: instanceof vs property in

HTML Preparation code:

<script>
class TestClass {
    constructor() {
        this.a = 2;
    }
}
</script>

Script Preparation code:

var obj = new TestClass();

Tests:

instanceof
obj instanceof TestClass;
property undefined
obj.a !== undefined
property in
'a' in obj

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
instanceof
property undefined
property in

Fastest: N/A

Slowest: N/A

Latest run results:

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

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:135.0) Gecko/20100101 Firefox/135.0

Browser/OS: Firefox 135 on Windows

View result in a separate tab

Test name	Executions per second
instanceof	154958880.0 Ops/sec
property undefined	1047604032.0 Ops/sec
property in	1335977600.0 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 benchmark and its options.

**Benchmark Definition**

The benchmark measures the performance of three different approaches:

1. **`instanceof` operator**: This operator checks if an object is an instance of a specific class or constructor.
2. **`property in` operator**: This operator checks if a property exists in an object, regardless of its type (i.e., whether it's a primitive value or an object itself).
3. **`property undefined` test**: This test checks if the property `a` is defined (i.e., not undefined) on the object.

**Options Comparison**

The `instanceof` operator and the `property in` operator are both used to check for properties existence, but they have different use cases:

* `instanceof` is typically used when you know the class or constructor you're looking for, as it provides more information about the type of object.
* `property in` is often used when you need to check if a property exists without knowing its type.

In this benchmark, both operators are being tested, but they have different execution profiles:

* `instanceof` typically requires a single lookup or call to the constructor's `hasOwnProperty()` method, making it relatively fast.
* `property in` can be slower because it needs to perform more operations, such as checking if the property exists on the object and its type.

**Pros and Cons**

Here are some pros and cons of each approach:

* **`instanceof` operator**:
	+ Pros: Fast, provides type information, often used for class-based checks.
	+ Cons: Can be slower for unknown types or when not knowing the exact constructor.
* **`property in` operator**:
	+ Pros: Flexible, can be used with any type of property, often used for generic existence checks.
	+ Cons: Slower due to additional operations, may require more memory accesses.

**Library and Special JS Features**

The benchmark uses JavaScript's built-in ` instanceof` and `in` operators. No special features or libraries are required beyond the standard JavaScript functionality.

**Other Considerations**

When dealing with object properties, it's essential to consider the following:

* **Property existence vs. value**: The `property in` operator checks for property existence, while the `instanceof` operator checks if the property has a specific value.
* **Object type and prototype chain**: When using `instanceof`, be aware that the constructor's prototype chain can affect the outcome.

**Alternatives**

If you're interested in exploring alternative approaches, here are some options:

* Use a library like Lodash to implement your own `property in` operator or improve existing ones.
* Experiment with newer JavaScript features like `Object.hasOwn()` (available in modern browsers) or `Reflect.has()` for more efficient property checks.
* Consider using a different data structure, such as a map or set, to store and retrieve properties for faster lookups.

Keep in mind that the choice of approach depends on your specific use case and requirements. Always test and optimize with your target audience in mind!

Related benchmarks:

instanceof vs property in (version: 0)

Measure the performance of instanceOf operator vs property in operator

Comparing performance of: instanceof vs property undefined vs property in

Created: 2 years ago by: Guest

Jump to the latest result

instanceof

property undefined

property in

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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