Benchmark: undefined vs. typeof vs. in vs. hasOwnPropertye

Script Preparation code:

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

Tests:

undefined
obj.d;
typeof
'undefined' !== typeof obj.d;
in
'd' in obj;
hasOwnProperty
obj.hasOwnProperty( 'd' );
bool
!! obj.d;

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
undefined
typeof
in
hasOwnProperty
bool

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 4 years ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/84.0.4147.125 Safari/537.36

Browser/OS: Chrome 84 on Windows

View result in a separate tab

Test name	Executions per second
undefined	8527941.0 Ops/sec
typeof	8524625.0 Ops/sec
in	8459198.0 Ops/sec
hasOwnProperty	7645408.0 Ops/sec
bool	8579742.0 Ops/sec

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

LLMs can make mistakes. Check important info.

Measuring the performance of different ways to check if an object has a property can be useful for optimizing code.

The provided JSON represents a benchmark test that compares five approaches:

1. **"obj.d;"** - Direct access to the property value, using the dot notation. This approach is simple and straightforward but may not work as expected if `d` is a function or an object.
2. **"'undefined' !== typeof obj.d;"** - Using the `typeof` operator to check if the property exists, comparing it with the string "undefined". The `typeof` operator returns a string indicating the type of the value, and in this case, "undefined" indicates that the property does not exist.
3. **"'d' in obj;"** - Using the `in` operator to check if the property is present in the object. This approach can be slower than the others because it has to iterate over the object's properties.
4. **"obj.hasOwnProperty( 'd' );"** - Using the `hasOwnProperty` method to check if the property exists only for the object that was passed to the function, with its own context. This approach is more accurate than the previous ones but can be slower.
5. **"!! obj.d;"** - Using a boolean cast to check if the property value is truthy. This approach assumes that an empty or null value has no effect on the execution of the code.

Now, let's discuss the pros and cons of each approach:

*   **Direct access ("obj.d;")**: Simple but may not work as expected for certain types of properties.
    *   Pros: Fastest execution
    *   Cons: May not work with functions or objects
*   **"typeof" comparison ("'undefined' !== typeof obj.d;"**): This approach can be slower than direct access, but it's more accurate when dealing with primitive values.
    *   Pros: Accurate for primitive values, relatively fast execution
    *   Cons: May be slower than direct access, requires string comparison
*   **"in" operator ("'d' in obj;"**): This approach can be slower due to its iteration mechanism but provides a way to check for the presence of properties.
    *   Pros: Can handle functions and objects, relatively accurate
    *   Cons: May be slower than direct access or "typeof" comparison, requires iteration over object properties
*   **"hasOwnProperty" method ("obj.hasOwnProperty( 'd' );"**): This approach is more accurate than the previous ones but can be slower.
    *   Pros: More accurate for objects and functions, relatively fast execution
    *   Cons: May be slower than direct access or "typeof" comparison, requires object context
*   **Boolean cast ("!! obj.d;"**): This approach assumes that an empty or null value has no effect on the execution of the code.
    *   Pros: Fastest execution, simple and concise
    *   Cons: May not be accurate for certain types of values (empty strings, numbers, etc.), relies on assuming a specific behavior

The test results indicate that the **"hasOwnProperty" method** is still one of the fastest approaches, despite its slight accuracy trade-off.

Other alternatives to these approaches include:

*   Using property existence operators like `in` or `hasOwnProperty`, which provide more control over the logic.
*   Creating a custom function for property checks, allowing for more flexibility and potentially better performance.
*   Using the `Object.prototype.hasOwnProperty.call()` method, which is slightly faster than `obj.hasOwnProperty( 'd' );`.

However, these alternatives should be considered on a case-by-case basis, taking into account the specific requirements of your project.

I hope this explanation helps software engineers understand the performance differences between various approaches to checking object property existence in JavaScript.

Related benchmarks:

undefined vs. typeof vs. in vs. hasOwnPropertye (version: 0)

Object lookup performance

Comparing performance of: undefined vs typeof vs in vs hasOwnProperty vs bool

Created: 4 years ago by: Guest

Jump to the latest result

undefined

typeof

in

hasOwnProperty

bool

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

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