Benchmark: tagName vs instanceof

Script Preparation code:

var xs = [];
var n = 0;

for (let i = 0; i < 1000; ++i) {
  xs[i] = (Math.random() > .5) ? document.createElement(`div`) : document.createElement(`span`);
};

Tests:

instanceof
n += ((xs[(Math.random() * 1000)|0]) instanceof HTMLDivElement)|0;
tagName
n += (xs[(Math.random() * 1000)|0].tagName === `DIV`)|0;
nodeName
n += (xs[(Math.random() * 1000)|0].nodeName === `DIV`)|0;
localName
n += (xs[(Math.random() * 1000)|0].localName === `div`)|0;
__proto__
n += ((xs[(Math.random() * 1000)|0]).__proto__ === HTMLDivElement.prototype)|0;

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
instanceof
tagName
nodeName
localName
__proto__

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 20 days ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/135.0.0.0 Safari/537.36

Browser/OS: Chrome 135 on Windows

View result in a separate tab

Test name	Executions per second
instanceof	7464936.0 Ops/sec
tagName	6362516.5 Ops/sec
nodeName	6286314.0 Ops/sec
localName	6576628.0 Ops/sec
__proto__	8552867.0 Ops/sec

Autogenerated LLM Summary (model llama3.2:3b, generated 6 months ago):

LLMs can make mistakes. Check important info.

Let's break down the provided JSON and explain what's being tested in this JavaScript microbenchmark.

**Benchmark Definition**

The benchmark is named "tagName vs instanceof" and has two main components:

1. **Script Preparation Code**: This code creates an array `xs` of 1000 elements, where each element is either a `<div>` or a `<span>` created using the `document.createElement()` method. The type of element is determined randomly.
2. **Html Preparation Code**: There is no HTML preparation code provided, which means that this benchmark doesn't require any specific HTML structure.

**Individual Test Cases**

The benchmark consists of five test cases, each with its own script:

1. **instanceof**
	* This test case checks if the element returned by `Math.random() * 1000 | 0` is an instance of `HTMLDivElement`. The `|` operator performs a bitwise XOR on the result of `Math.random()` and 1000, which ensures that the index into the array is either even or odd. This is done to randomly select between two types of elements.
2. **tagName**
	* This test case checks if the element returned by `Math.random() * 1000 | 0` has a `tagName` property equal to "DIV".
3. **nodeName**
	* Similar to the previous test, but it checks if the element's `nodeName` property is equal to "DIV".
4. **localName**
	* This test case checks if the element's `localName` property (a CSS property) is equal to "div" (note the lowercase "d").
5. **__proto__**
	* This test case checks if the element returned by `Math.random() * 1000 | 0` has its prototype chain equal to that of `HTMLDivElement.prototype`.

**Pros and Cons**

Each approach has its pros and cons:

1. **instanceof**: This method is generally the most efficient way to check the type of an object in JavaScript, as it uses a special optimized implementation.
	* Pros: Fast, reliable, and widely supported.
	* Cons: May not work correctly for certain types of objects (e.g., functions) or unexpected use cases.
2. **tagName**: This method is specific to DOM elements and may not be suitable for other types of objects.
	* Pros: Simple and effective for DOM elements, but may not generalize well to other contexts.
	* Cons: Limited by the scope of the `tagName` property, which only applies to DOM elements.
3. **nodeName**: Similar to `tagName`, this method is specific to DOM elements and has its own limitations.
4. **localName**: This method is also specific to CSS properties and may not be suitable for other types of objects or contexts.
5. **__proto__**: This method relies on the object's prototype chain, which can lead to unexpected behavior if not used carefully.
	* Pros: Can provide fine-grained control over type checking, but requires more expertise and care.

**Library**

None of these methods rely on a specific library or framework. However, for DOM-related operations, libraries like jQuery or DOM manipulation functions provided by browsers (e.g., `document.createElement()` in this case) are often used.

**Special JS Features/Syntax**

There is no special JavaScript feature or syntax that requires particular attention or expertise. The benchmark focuses on the comparison of these five methods for type checking, which can be applied to various contexts.

**Alternatives**

Other alternatives for type checking in JavaScript include:

1. `typeof` operator: This method provides a more general-purpose way to check the type of an object.
2. Function prototypes (e.g., `Object.prototype.toString()`): This approach can provide more detailed information about an object's type, but may be slower and less reliable than `instanceof`.
3. Custom solutions using bitwise operations or regex patterns: These alternatives can offer fine-grained control over type checking, but often come with additional complexity and potential pitfalls.

In summary, the benchmark tests five common methods for type checking in JavaScript: `instanceof`, `tagName`, `nodeName`, `localName`, and `__proto__`. While each approach has its pros and cons, `instanceof` is generally considered the most efficient and reliable method.

Related benchmarks:

tagName vs instanceof (version: 0)

Comparing performance of: instanceof vs tagName vs nodeName vs localName vs proto

Created: 5 years ago by: Registered User

Jump to the latest result

instanceof

tagName

nodeName

localName

proto

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 6 months ago):

tagName vs instanceof (version: 0)

Comparing performance of: instanceof vs tagName vs nodeName vs localName vs __proto__

Created: 5 years ago by: Registered User

Jump to the latest result

instanceof

tagName

nodeName

localName

__proto__

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 6 months ago):

Comparing performance of: instanceof vs tagName vs nodeName vs localName vs proto

proto