Benchmark: undefined vs. typeof vs. in vs. hasOwnProperty vs exists vs double bang

Script Preparation code:

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

Tests:

undefined
undefined !== obj.d;
typeof
'undefined' !== typeof obj.d;
in
'd' in obj;
hasOwnProperty
obj.hasOwnProperty( 'd' );
double bang
!! obj.d;
exists
obj.d;

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
undefined
typeof
in
hasOwnProperty
double bang
exists

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 23 days ago):

LLMs can make mistakes. Check important info.

Let's break down the provided benchmark and explain what's being tested.

**Benchmark Overview**

The benchmark measures the performance of different ways to check if a property exists in an object or retrieve its value. The test cases are:

1. `undefined !== obj.d;` (Checking if `obj.d` is undefined)
2. `'undefined' !== typeof obj.d;` (Comparing 'undefined' with the type of `obj.d`)
3. `'d' in obj;` (Using the 'in' operator to check if 'd' exists in the object)
4. `obj.hasOwnProperty('d');` (Checking if 'd' is a direct property of `obj`)
5. `!! obj.d;` (Double-boolean bang! Checking if `obj.d` is truthy)
6. `obj.d;` (Simply accessing the value of `obj.d`)

**Library and Special Features**

None of these test cases rely on any specific libraries or special JavaScript features beyond basic object property access.

**Options Compared**

The benchmark compares six different approaches to check if a property exists in an object or retrieve its value. Each test case measures the performance of one particular approach, while others serve as controls:

* `undefined !== obj.d;` and `!! obj.d;` compare checking for existence with explicit boolean evaluation.
* `'undefined' !== typeof obj.d;` compares type checking (typeof) to direct property access.
* `'d' in obj;` uses the 'in' operator, which is a built-in method that returns a boolean indicating whether the specified property exists in the object.
* `obj.hasOwnProperty('d');` checks if 'd' is a direct property of `obj`, using the `hasOwnProperty` method.

**Pros and Cons of Each Approach**

Here's a brief overview:

1. **Direct Property Access (`obj.d;`)**: Fast, but may throw an error if `obj.d` doesn't exist.
	* Pros: Simple, efficient
	* Cons: May throw errors
2. **'in' Operator (`'d' in obj;`)**: Returns a boolean value indicating existence, without throwing errors.
	* Pros: Safe, returns a boolean
	* Cons: May be slower than direct access due to the overhead of checking for existence
3. **Type Checking (`typeof obj.d === 'undefined';`)**: Compares the type of `obj.d` with 'undefined', which may not cover all cases (e.g., null).
	* Pros: Useful for detecting specific types, but less reliable than direct access or 'in' operator
	* Cons: May return false positives or negatives
4. **HasOwnProperty (`obj.hasOwnProperty('d');`)**: Checks if `d` is a direct property of `obj`, which may not cover inherited properties.
	* Pros: Reliable for checking direct properties, but may be slower than 'in' operator due to the overhead of method calls
	* Cons: May return false positives or negatives on inherited properties

**Other Considerations**

When writing performance-critical code, consider the following:

* Avoid using `typeof` when you only need to check if a value is an object (e.g., checking if an array has more than one element).
* Use the 'in' operator when you need to check if a property exists in an object, especially for properties with dynamic names.
* For simple cases where direct access is safe and efficient, use direct property access (`obj.d;`) or `!! obj.d;` to avoid unnecessary checks.

**Alternatives**

If this benchmark were conducted on another platform or using different JavaScript versions, you might see variations in performance due to differences in:

* Language features: Some browsers may implement certain language features (e.g., `const` declarations) more efficiently than others.
* Optimizations: Browsers may use various optimizations (e.g., caching, just-in-time compilation) that affect performance.
* Hardware and software configurations: Different hardware and software configurations can impact the performance of JavaScript engines.

In conclusion, this benchmark provides a valuable insight into the performance characteristics of different approaches to checking property existence in objects. By understanding these differences, developers can optimize their code for better performance on various browsers and platforms.

Latest run results:

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

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:109.0) Gecko/20100101 Firefox/119.0

Browser/OS: Firefox 119 on Mac OS X 10.15

View result in a separate tab

Test name	Executions per second
undefined	798379776.0 Ops/sec
typeof	813430528.0 Ops/sec
in	799115264.0 Ops/sec
hasOwnProperty	808549824.0 Ops/sec
double bang	809473792.0 Ops/sec
exists	809339840.0 Ops/sec

Related benchmarks:

undefined vs. typeof vs. in vs. hasOwnProperty vs exists vs double bang (version: 0)

Object lookup performance

Comparing performance of: undefined vs typeof vs in vs hasOwnProperty vs double bang vs exists

Created: 6 years ago by: Guest

Jump to the latest result

undefined

typeof

in

hasOwnProperty

double bang

exists

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 23 days ago):