Benchmark: jsj2 undefined vs. typeof vs. in vs. hasOwnProperty

Script Preparation code:

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

Tests:

typeof a.1
typeof obj.d === 'undefined'
typeof b.1
'undefined' === typeof obj.d;
typeof a.2
typeof obj.d === 'undefined'
typeof b.2
'undefined' === typeof obj.d;
typeof a.3
typeof obj.d === 'undefined'
typeof b.3
'undefined' === typeof obj.d;

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
typeof a.1
typeof b.1
typeof a.2
typeof b.2
typeof a.3
typeof b.3

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 dive into the world of JavaScript microbenchmarks.

**Benchmark Definition**

The provided JSON represents a benchmark test case on `MeasureThat.net`. The test is designed to measure the performance of different methods for checking if a property exists in an object. Specifically, it tests four methods:

1. `typeof` operator
2. String equality check (`'undefined' === typeof obj.d`)
3. `in` operator
4. `hasOwnProperty` method

The benchmark aims to understand which approach is the most efficient.

**Options Compared**

Here's a brief overview of each option compared in this test:

1. **typeof**: This method checks if an object has a property with the given name using the `Object.prototype.toString()` method. It returns either the type of the property (e.g., "number", "string") or "undefined" if the property does not exist.
2. **String equality check**: This method compares the result of `typeof obj.d` to the string `'undefined'`. If they are equal, it assumes that the property does not exist.
3. **in** operator: This method checks if a given name exists in an object using the `in` keyword. It returns true if the property exists and false otherwise.
4. **hasOwnProperty**: This method is part of the Object prototype and returns true if the object has the specified property as its own property (i.e., not inherited from another object).

**Pros and Cons**

Here's a brief summary of the pros and cons of each approach:

1. **typeof**:
	* Pros: Simple, widely supported, and efficient.
	* Cons: May return incorrect results for some types (e.g., null or undefined), and can be slower than other methods.
2. **String equality check**:
	* Pros: Fast and accurate for most cases.
	* Cons: May be slower due to the string comparison, and requires careful handling of edge cases.
3. **in** operator:
	* Pros: Fast and widely supported.
	* Cons: May be slower than `typeof` or string equality check for some browsers, and can return unexpected results if not used carefully.
4. **hasOwnProperty**:
	* Pros: Accurate and fast for most cases.
	* Cons: Less widely supported than other methods, as it's only available on the Object prototype.

**Library Used**

None of the above methods rely on a specific library. However, `typeof` is often used in conjunction with the `Object.prototype.toString()` method, which is part of the ECMAScript specification.

**Special JS Feature or Syntax**

This benchmark does not use any special JavaScript features or syntax beyond what's covered by the ECMAScript specification.

Now that we've explored the benchmark definition and options compared, let's look at some alternatives:

* Other methods for checking property existence, such as using a regex or a custom function.
* Using libraries like Lodash or Underscore.js, which provide additional utility functions for working with objects.
* Implementing custom optimizations for specific use cases.

Keep in mind that the choice of approach depends on the specific requirements and constraints of your project.

Related benchmarks:

jsj2 undefined vs. typeof vs. in vs. hasOwnProperty (version: 0)

Object lookup performance

Comparing performance of: typeof a.1 vs typeof b.1 vs typeof a.2 vs typeof b.2 vs typeof a.3 vs typeof b.3

Created: 7 years ago by: Guest

Jump to the latest result

typeof a.1

typeof b.1

typeof a.2

typeof b.2

typeof a.3

typeof b.3

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):