Benchmark: undefined vs typeof vs in vs hasOwnProperty vs bool

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;
Object.hasOwnProperty
Object.hasOwn(obj, 'd')
optional chaining undefined
obj?.z !== 'undefined'

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
undefined
typeof
in
hasOwnProperty
bool
Object.hasOwnProperty
optional chaining undefined

Fastest: N/A

Slowest: N/A

Latest run results:

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

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/131.0.0.0 Safari/537.36

Browser/OS: Chrome 131 on Windows

View result in a separate tab

Test name	Executions per second
undefined	9955479.0 Ops/sec
typeof	18914318.0 Ops/sec
in	18712574.0 Ops/sec
hasOwnProperty	17650708.0 Ops/sec
bool	18642852.0 Ops/sec
Object.hasOwnProperty	9341534.0 Ops/sec
optional chaining undefined	18910246.0 Ops/sec

Autogenerated LLM Summary (model gpt-4o-mini, generated 28 days ago):

LLMs can make mistakes. Check important info.

The benchmark in question tests the performance of various methods for checking the existence of a property in a JavaScript object. The options compared in this benchmark are:

1. **undefined**: `undefined !== obj.d;`
   - **Pros**: This approach is simple and straightforward. It only checks whether accessing the property `d` returns `undefined`, which effectively implies that the property does not exist.
   - **Cons**: This method does not differentiate between a non-existent property and one that exists but has an explicit value of `undefined`. Hence, it may lead to misinterpretations in scenarios where the property exists but hasn't been assigned a value.

2. **typeof**: `'undefined' !== typeof obj.d;`
   - **Pros**: This method is more reliable because it checks the type of the property. If the property does not exist, `typeof` safely returns `'undefined'` without raising an error.
   - **Cons**: This approach has a slight overhead due to the type checking, making it marginally slower than checking directly against `undefined` in certain contexts.

3. **in**: `'d' in obj;`
   - **Pros**: This checks for the property’s existence in the object’s prototype chain, making it comprehensive. It can distinguish between properties that exist and those that don't, regardless of their values.
   - **Cons**: It may return true for properties that are inherited from the object's prototype, which might not be desirable in all cases.

4. **hasOwnProperty**: `obj.hasOwnProperty('d');`
   - **Pros**: Using `hasOwnProperty` directly checks if the property belongs to the object itself, excluding inherited properties. This is useful for instances where prototype pollution could lead to misleading results.
   - **Cons**: It requires a method call and could be slightly slower compared to the simpler checks. Also, if the method is overridden in the object, it may not behave as expected.

5. **bool**: `!!obj.d;`
   - **Pros**: This approach quickly checks if the property evaluates to a truthy value. It provides an immediate result without needing a method or operator.
   - **Cons**: It does not distinguish between properties that have values of `0`, `false`, `null`, or `undefined`, which could lead to incorrect conclusions about whether a property exists.

6. **Object.hasOwn**: `Object.hasOwn(obj, 'd');`
   - **Pros**: This is a relatively newer method that provides a clear and efficient way to check an object's own properties.
   - **Cons**: Availability may be an issue in older environments that do not support this method.

7. **Optional chaining**: `obj?.z !== 'undefined'`
   - **Pros**: This approach safely accesses the property and returns `undefined` without throwing an error if `obj` is null or undefined. It simplifies some checks but serves a different purpose by allowing for safe navigation through nested properties.
   - **Cons**: The comparison to a string literal (`'undefined'`) at the end might lead to confusion; this might not be as commonly used for existence checks.

### Benchmark Results
From the benchmark results, it is observed that the fastest method was `typeof`, followed closely by `optional chaining`, `in`, and `bool`. The slowest were `undefined` and `Object.hasOwnProperty`.

### Other Considerations and Alternatives
1. **Performance**: The performance metrics indicate how many executions per second each method can perform. Depending on the specific use case and the number of checks executed in rapid succession, performance can greatly impact application efficiency.

2. **Readability and Maintainability**: The choice of method might also depend on the coding standards of a project or team. Some developers might prioritize clarity and explicitness over micro-optimizations.

3. **Older Browsers Compatibility**: Some methods like `Object.hasOwn` and modern shorthand or new features may not be supported in older JavaScript environments, which would guide developers towards more traditional approaches.

4. **Alternative Libraries/Frameworks**: In larger applications, especially those utilizing libraries like Lodash, you can perform checks using methods like `_.has(obj, 'd')` for a more robust and simple syntax, providing cross-environment compatibility.

In conclusion, when choosing a method for property existence checks in JavaScript, consider both performance implications and the specific behavior required in your application context, balancing trade-offs between speed, clarity, and behavior nuances.

Related benchmarks:

undefined vs typeof vs in vs hasOwnProperty vs bool (version: 1)

Object lookup performance

Comparing performance of: undefined vs typeof vs in vs hasOwnProperty vs bool vs Object.hasOwnProperty vs optional chaining undefined

Created: one month ago by: Guest

Jump to the latest result

undefined

typeof

in

hasOwnProperty

bool

Object.hasOwnProperty

optional chaining undefined

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model gpt-4o-mini, generated 28 days ago):