Benchmark: in vs. hasOwnProperty

Script Preparation code:

var obj = { a: 1, b: 2, c: 3, d: 4, e: 5 };

Tests:

in
'd' in obj;
hasOwnProperty
obj.hasOwnProperty( 'd' );

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
in
hasOwnProperty

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 the provided JSON and explain what's being tested, compared, and some pros/cons of each approach.

**Benchmark Definition**

The benchmark measures the performance of two different approaches to check if a key exists in an object:

1. **`'d' in obj`**: This uses the `in` operator to check if the string `'d'` is a property of the `obj` object.
2. **`obj.hasOwnProperty( 'd' )`**: This uses the `hasOwnProperty` method of the object, which checks if the specified property is an own property (i.e., not inherited from the prototype chain).

**Options Compared**

The two options are compared in terms of performance.

**Pros and Cons of Each Approach**

1. **`'d' in obj`**:
	* Pros: Simple, efficient, and widely supported.
	* Cons: May be slower than `hasOwnProperty` for large objects or when the property is not found, as it requires a linear search through the object's properties.
2. **`obj.hasOwnProperty( 'd' )`**:
	* Pros: More accurate for large objects or when checking if a property is an own property.
	* Cons: May be slower than `in` due to the method call and additional checks.

**Library Used**

None, this benchmark uses native JavaScript features only.

**Special JS Features/Syntax**

Neither of these approaches uses any special JavaScript features or syntax. They are both part of the standard language.

**Other Alternatives**

If you're interested in exploring other options:

* **`Object.prototype.hasOwnProperty.call(obj, 'd')`**: This is a similar approach to `hasOwnProperty`, but it relies on the `call` method and the prototype chain.
* **`Array.isArray()` or `typeof` checks**: While not directly applicable to objects, these can be used to check if a value is an array or object, respectively.

In general, for simple cases where performance is not critical, using `in` might be sufficient. However, when dealing with large objects or requiring more precision, `hasOwnProperty` or alternative approaches like `Object.prototype.hasOwnProperty.call(obj, 'd')` may be preferable.

Latest run results:

Run details: (Test run date: 2 months ago)

User agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/128.0.0.0 Safari/537.36

Browser/OS: Chrome 128 on Linux

View result in a separate tab

Test name	Executions per second
in	16260021.0 Ops/sec
hasOwnProperty	14818578.0 Ops/sec

Related benchmarks:

in vs. hasOwnProperty (version: 0)

Object lookup performance

Comparing performance of: in vs hasOwnProperty

Created: 2 years ago by: Guest

Jump to the latest result

in

hasOwnProperty

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):