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

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' );

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
undefined
typeof
in
hasOwnProperty

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 26 days ago):

LLMs can make mistakes. Check important info.

**Benchmark Overview**

The provided benchmark measures the performance of four different approaches for checking if a property exists in an object:

1. `typeof`
2. `in`
3. `hasOwnProperty`
4. Direct equality check (`===`)

**Options Comparison**

Here's a brief overview of each option and their pros and cons:

* **Direct Equality Check (`===`)**: This approach checks for exact equality between the property name and the object's property.
	+ Pros: Simple, fast, and widely supported.
	+ Cons: Can be slow due to string comparison overhead. May not work correctly with special characters or complex objects.
* **`typeof`**: This operator returns a string indicating the type of the property (e.g., "number", "string", etc.). However, it also returns "object" for non-primitive values.
	+ Pros: Fast and lightweight, but may return incorrect results for certain data types.
	+ Cons: Can be misleading due to its behavior with objects.
* **`in`**: This operator checks if a property exists in the object using the bracket notation (e.g., `obj["d"] != undefined;`).
	+ Pros: Fast and widely supported, but may require explicit property names.
	+ Cons: May not work correctly with special characters or complex objects.
* **`hasOwnProperty`**: This method is specifically designed for checking if a property exists in an object. It returns `true` if the property exists and `false` otherwise.
	+ Pros: Fast, accurate, and specifically designed for this purpose.
	+ Cons: May be slower than direct equality check or `in`, but still relatively fast.

**Library Usage**

In the provided benchmark code, no libraries are used explicitly. However, some browser-specific features like `typeof` might rely on underlying libraries or engine-specific optimizations.

**Special JavaScript Features**

None of the special JavaScript features are mentioned in the provided code or data. If any were present, they would be worth noting for completeness.

**Other Alternatives**

In addition to the four approaches listed above, there are other ways to check if a property exists in an object:

* Using a library like Lodash (`_.has()` method)
* Implementing your own custom solution using bitwise operations or string manipulation
* Utilizing browser-specific features like `Object.keys()` or `Array.prototype.includes()`

Keep in mind that these alternatives might have varying performance characteristics and trade-offs, depending on the specific use case.

**Benchmark Results**

The provided benchmark results show the execution times for each approach:

| Approach | Execution Time (ExecutionsPerSecond) |
| --- | --- |
| typeof | 11418497.0 |
| hasOwnProperty | 11318011.0 |
| in | 11318011.0 |
| Direct Equality Check (`===`) | 3805573.5 |

These results suggest that `hasOwnProperty` and `in` are the fastest approaches, followed closely by `typeof`. The direct equality check is significantly slower due to its string comparison overhead.

It's worth noting that these results may vary depending on the specific browser version, platform, and hardware used for testing.

Latest run results:

Run details: (Test run date: 7 years ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_3) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/55.0.2883.95 Safari/537.36

Browser/OS: Chrome 55 on Mac OS X 10.12.3

View result in a separate tab

Test name	Executions per second
undefined	3805573.5 Ops/sec
typeof	11995687.0 Ops/sec
in	11318011.0 Ops/sec
hasOwnProperty	11418497.0 Ops/sec

Related benchmarks:

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

Object lookup performance

Comparing performance of: undefined vs typeof vs in vs hasOwnProperty

Created: 7 years ago by: Guest

Jump to the latest result

undefined

typeof

in

hasOwnProperty

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 26 days ago):