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' );
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: an hour ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/135.0.0.0 Safari/537.36

Browser/OS: Chrome 135 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
undefined	175738192.0 Ops/sec
typeof	186299600.0 Ops/sec
in	136637872.0 Ops/sec
hasOwnProperty	121787272.0 Ops/sec
bool	179997088.0 Ops/sec

Autogenerated LLM Summary (model llama3.2:3b, generated 6 months ago):

LLMs can make mistakes. Check important info.

**Benchmark Overview**

The provided benchmark measures the performance of different JavaScript operators for object lookup: `undefined`, `typeof`, `in`, `hasOwnProperty`, and a boolean test (`!! obj.d;`).

**Operator Comparison**

Here's an explanation of each operator, their pros and cons, and alternative approaches:

1. **Undefined (`undefined !== obj.d;`)**
	* This operator checks if the variable `obj.d` has been assigned a value (i.e., is not `undefined`). It's often used to avoid errors when accessing object properties.
	* Pros: Simple and straightforward.
	* Cons: Can be slower due to the explicit check.
	* Alternative approach: Use the optional chaining operator (`?.`) introduced in ECMAScript 2020, which allows safe navigation of nested objects without throwing an error. Example: `obj?.d;`
2. **typeof (`'undefined' !== typeof obj.d;`)**
	* This operator checks if the type of `obj.d` is indeed `undefined`.
	* Pros: More explicit and safer than using the `===` operator.
	* Cons: Can be slower due to the additional comparison.
	* Alternative approach: Use the optional chaining operator (`?.`) instead, which provides similar functionality without the need for `typeof`. Example: `'?' in obj;`
3. **in (`'d' in obj;`)**
	* This operator checks if the property `'d'` exists in the object `obj`.
	* Pros: Similar to `hasOwnProperty`, but returns a boolean value.
	* Cons: Can be slower due to the additional lookup.
	* Alternative approach: Use the optional chaining operator (`?.`) instead, which provides similar functionality without the need for `in`. Example: `obj['d'] !== undefined;`
4. **hasOwnProperty (`obj.hasOwnProperty( 'd' );`)**
	* This operator checks if the property `'d'` exists in the object `obj` and was not inherited from a parent object.
	* Pros: More accurate than using `in`, as it excludes inherited properties.
	* Cons: Can be slower due to the additional check.
	* Alternative approach: Use the optional chaining operator (`?.`) instead, which provides similar functionality without the need for `hasOwnProperty`. Example: `obj['d'] !== undefined;`

**Library and Special JS Features**

The benchmark uses no external libraries or special JavaScript features. The only notable feature is the use of `!! obj.d;`, which is a boolean test that evaluates to `true` if `obj.d` has any truthy value (e.g., number, string, object). This test is not specific to any particular library or syntax.

**Other Alternatives**

Some alternative approaches for object lookup can be found in other languages:

* In Python, you would use the `.get()` method: `obj.get('d', None)`
* In Java, you would use the `instanceof` operator: `obj instanceof Object && obj instanceof MyObject`

Keep in mind that these alternatives may have different performance characteristics and are not directly equivalent to the JavaScript operators being tested.

**Benchmark Conclusion**

The benchmark provides a good overview of the performance differences between various object lookup methods in JavaScript. However, it's essential to note that the results may vary depending on specific use cases, object structures, and browser implementations.

Related benchmarks:

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

Object lookup performance

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

Created: 8 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 6 months ago):