Benchmark: jsj 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;
undefined2
typeof obj.d === 'undefined';

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
undefined
typeof
in
hasOwnProperty
bool
undefined2

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 28 days ago):

LLMs can make mistakes. Check important info.

Let's break down what's being tested on the provided JSON.

**Benchmark Definition**

The benchmark is designed to compare the performance of different ways to check if a property exists or has a specific value in an object. The properties are "undefined", "typeof obj.d", "in", and "hasOwnProperty".

**Options Compared**

Here's a brief overview of each option being compared:

1. **`undefined === obj.d`**: This is the most straightforward way to check if `obj.d` has no value (i.e., it's undefined). It checks if both sides of the comparison are equal.
2. **`'undefined' === typeof obj.d`**: This uses the `typeof` operator to get the type of `obj.d`, which will return `"undefined"` because `obj.d` is an empty string. The comparison then checks if this type is equal to the literal string `'undefined'`.
3. **`!('d' in obj)`**: This uses the "not in" operator (`!in`) to check if there's no property named `'d'` in the object `obj`. The `!` negates the result, so the expression becomes true if `d` is not found.
4. **`!obj.hasOwnProperty('d')`**: This checks if `obj` has a property named `'d'` using the `hasOwnProperty` method. If `obj.d` exists, this will return false.
5. **`! obj.d`**: This simply negates the value of `obj.d`, effectively checking if it's not equal to any number (since it's an empty string). The expression is true if `d` has no value.

**Pros and Cons**

Here are some pros and cons for each approach:

1. **`undefined === obj.d`**: Pros: Simple, straightforward. Cons: May have performance issues due to the type coercion.
2. **`'undefined' === typeof obj.d`**: Pros: More robust than `!obj.d`, handles cases where `d` is an empty string. Cons: Uses `typeof` operator, which can introduce overhead.
3. **`!('d' in obj)`**: Pros: Fast and simple. Cons: May not be as readable or maintainable as other options.
4. **`!obj.hasOwnProperty('d')`**: Pros: Safe from cases where `d` is an empty string (i.e., it doesn't have a property with that name). Cons: Uses `hasOwnProperty`, which can be slower than the other options.
5. **`! obj.d`**: Pros: Simple and fast. Cons: May not handle all edge cases correctly.

**Library and Purpose**

None of these approaches require any external libraries or modules.

**Special JS Feature or Syntax**

The "not in" operator (`!in`) is a feature introduced in ECMAScript 2009 (ES5). It's also available as the `!!` operator, which can be used for similar purposes. The `hasOwnProperty` method is an instance method of objects and returns a boolean value.

**Other Alternatives**

If you're interested in exploring alternative approaches or optimizations, here are some additional options:

1. **Use `Object.hasOwn()` instead of `hasOwnProperty()`:** This newer method provides more flexibility and accuracy.
2. **Use `in` with parentheses:** Some developers argue that using parentheses around the property name (`('d' in obj)`) improves readability.
3. **Use a library or framework-specific solution:** If you're working with a specific JavaScript library or framework, there might be built-in solutions for this problem.

Keep in mind that these alternatives may not provide significant performance improvements over the original options but can offer improved code quality and maintainability.

Latest run results:

Run details: (Test run date: 5 years ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_3) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/73.0.3683.75 Safari/537.36

Browser/OS: Chrome 73 on Mac OS X 10.14.3

View result in a separate tab

Test name	Executions per second
undefined	4648857.5 Ops/sec
typeof	14641496.0 Ops/sec
in	13467061.0 Ops/sec
hasOwnProperty	13059524.0 Ops/sec
bool	14518371.0 Ops/sec
undefined2	14556754.0 Ops/sec

Related benchmarks:

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

Object lookup performance

Comparing performance of: undefined vs typeof vs in vs hasOwnProperty vs bool vs undefined2

Created: 5 years ago by: Guest

Jump to the latest result

undefined

typeof

in

hasOwnProperty

bool

undefined2

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 28 days ago):