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

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' );
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

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

LLMs can make mistakes. Check important info.

The provided JSON represents a JavaScript microbenchmark that tests the performance of different ways to check if a property exists in an object. The benchmark compares four approaches:

1. **`in` operator**: Checks if a property exists by using the `in` operator with the object and the property name as arguments.
2. **`hasOwnProperty()` method**: A method provided by objects that checks if the object has a property with the given name, returning `true` if it does and `false` otherwise.
3. **Type checking with `typeof`**: Compares the result of using `typeof` to check if the property exists (in this case, checking if the value is not "undefined" or null).
4. **Direct equality check (`===`) on a boolean value**: Creates a boolean value indicating whether the property exists and then checks if it's equal to another value.

Let's examine each approach:

**Pros and Cons:**

*   **`in` operator**:
    *   Pros: Simple, intuitive syntax; often preferred by developers due to its simplicity.
    *   Cons: May not be as efficient as other methods for large objects or complex property names.
*   **`hasOwnProperty()` method**:
    *   Pros: Provides a more robust way of checking if an object has a specific property, as it also checks for prototype chain inheritance.
    *   Cons: Requires the use of `this` and may not be suitable for all scenarios (e.g., when dealing with primitive values or array indices).
*   **Type checking with `typeof`**:
    *   Pros: Can provide an additional layer of error checking by verifying the type of the result, making it easier to identify potential issues.
    *   Cons: May not be as efficient as other methods and can lead to false negatives if used incorrectly (e.g., checking for a non-boolean value).
*   **Direct equality check (`===`) on a boolean value**:
    *   Pros: Provides a clear indication of whether the property exists or not, making it easier to understand the outcome.
    *   Cons: Creates unnecessary computations and can lead to performance issues for large datasets.

**Additional Considerations:**

In addition to these methods, there are other ways to check if an object has a specific property. For example, you could use `Object.prototype.hasOwnProperty.call()` or `in` with an array index (e.g., `[obj.length - 1] in obj`). However, these alternatives may not be as readable or efficient as the ones mentioned above.

**Library Usage:**

None of the provided methods rely on external libraries. The `hasOwnProperty()` method is a built-in object method, while the others use basic JavaScript operators and syntax.

**Special JS Features/Syntax:**

There are no special JavaScript features or syntax used in this benchmark that would make it unique or require a specific level of expertise to understand.

In summary, the provided JSON represents a simple yet informative benchmark that allows users to compare the performance of different methods for checking if an object has a specific property. By understanding the pros and cons of each approach, developers can make informed decisions about which method to use in their own projects based on performance requirements and readability considerations.

Latest run results:

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

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/111.0.0.0 Safari/537.36

Browser/OS: Chrome 111 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
undefined	10391974.0 Ops/sec
typeof	28945272.0 Ops/sec
in	28846120.0 Ops/sec
hasOwnProperty	25095666.0 Ops/sec
bool	28803180.0 Ops/sec

Related benchmarks:

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

Object lookup performance

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

Created: one year 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 one month ago):