Benchmark: undefined vs. typeof vs. in vs. hasOwnProperty (missing key)

Script Preparation code:

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

Tests:

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

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: 3 years ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/88.0.4324.192 Safari/537.36

Browser/OS: Chrome 88 on Windows

View result in a separate tab

Test name	Executions per second
undefined	3401755.8 Ops/sec
typeof	9781481.0 Ops/sec
in	9862545.0 Ops/sec
hasOwnProperty	8620105.0 Ops/sec
bool	9639830.0 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's dive into the explanation of the provided benchmark.

**Benchmark Definition**

The benchmark measures the performance of different methods for checking if a key exists in an object. The test case uses a single object `obj` with five properties: `a`, `b`, `c`, `d`, and `e`. The benchmark defines four different scenarios:

1. `undefined === obj.f;`: This tests whether accessing a non-existent property (`obj.f`) using the `===` operator returns `false`.
2. `'undefined' === typeof obj.f;`: This tests whether comparing an empty string (`'undefined'`) to the result of the `typeof` operator on `obj.f` returns `true`.
3. `!('f' in obj);`: This tests whether negating the result of the `in` operator on the property name `'f'` returns `false`.
4. `!obj.hasOwnProperty('f');`: This tests whether negating the result of calling the `hasOwnProperty` method on the object with the key `'f'` returns `true`.
5. `! obj.f;`: This is a simple check for an empty boolean value, effectively testing if the property does not exist.

**Options Compared**

The benchmark compares the performance of the following options:

1. `undefined === obj.f`
2. `'undefined' === typeof obj.f`
3. `!('f' in obj)`
4. `!obj.hasOwnProperty('f')`
5. `! obj.f`

Each option is tested using a different approach:

* Options 1 and 2 use the `===` operator or a comparison with an empty string.
* Option 3 uses the `in` operator.
* Option 4 calls the `hasOwnProperty` method on the object.
* Option 5 checks for an empty boolean value.

**Pros and Cons**

Here's a brief analysis of each option:

1. **`undefined === obj.f`**: This is the most efficient approach, as it uses a simple comparison with `undefined`. However, it may not work correctly if `obj.f` is set to a non-empty value.
2. **`'undefined' === typeof obj.f`**: This approach works for all cases, but it's slower than the first option due to the additional string comparison.
3. **`!('f' in obj)`**: The `in` operator can be slow if used on large objects or arrays. Additionally, this approach returns a boolean value, which may not be desirable depending on the context.
4. **`!obj.hasOwnProperty('f')`**: This method is more efficient than using `in`, but it requires checking the property's existence manually. It also assumes that the object has the desired property.
5. **`! obj.f;`**: This approach checks for an empty boolean value, which may not be relevant in most cases.

**Library Usage**

None of the options require any additional libraries or dependencies.

**Special JS Features/Syntax**

There are no special JavaScript features or syntax used in this benchmark. The tests only use standard JavaScript operators and methods.

**Alternatives**

Other alternatives to check if a key exists in an object include:

1. `Object.hasOwn(obj, 'f')`: This method is similar to `hasOwnProperty`, but it returns `true` even if the property is inherited from another object.
2. `obj['f'] !== undefined`: This approach uses bracket notation and checks for an empty value.

In general, the choice of approach depends on the specific use case and performance requirements. If you need to check for a key existence in a large object or array, using `in` or `hasOwnProperty` might be necessary. However, if you can avoid using these methods due to performance constraints, `undefined === obj.f` or similar approaches may be more suitable.

Related benchmarks:

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

Object lookup performance

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

Created: 3 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):