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

Latest run results:

No previous run results

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Autogenerated LLM Summary (model llama3.2:3b, generated one year 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.

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: 7 years ago by: Guest

Jump to the latest result

undefined

typeof

in

hasOwnProperty

bool

undefined2

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

No previous run results

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