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cssRule Identify the type
(version: 0)
Comparing performance of:
type vs instanceof vs toString
Created:
4 years ago
by:
Registered User
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HTML Preparation code:
<html> <style> html { color: red; } </style> </html>
Script Preparation code:
window.myRules = document.styleSheets[0].cssRules;
Tests:
type
myRules[0].type === 1
instanceof
myRules[0] instanceof CSSStyleRule
toString
myRules[0].toString() === '[object CSSStyleRule]'
Rendered benchmark preparation results:
Suite status:
<idle, ready to run>
Run tests (3)
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Test case name
Result
type
instanceof
toString
Fastest:
N/A
Slowest:
N/A
Latest run results:
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Autogenerated LLM Summary
(model
llama3.2:3b
, generated one year ago):
Let's break down what's being tested in this benchmark and explore the options, pros, cons, and other considerations. **Benchmark Definition** The benchmark is testing the type of a CSS rule on a web page. Specifically, it creates a stylesheet and retrieves its first rule using `window.myRules = document.styleSheets[0].cssRules;`. The benchmark then checks three different conditions: 1. `myRules[0].type === 1` 2. `myRules[0] instanceof CSSStyleRule` 3. `myRules[0].toString() === '[object CSSStyleRule]'` These conditions test whether the rule is of type 1 (a `CSSStyleRule`), an instance of `CSSStyleRule`, and whether its string representation matches the expected format. **Options compared** The benchmark is comparing three different approaches to check the type of a CSS rule: 1. **Type checking (`myRules[0].type === 1`)**: This checks if the `type` property of the rule is exactly equal to 1. 2. **Instance checking (`myRules[0] instanceof CSSStyleRule`)**: This checks if the rule is an instance of the `CSSStyleRule` class. 3. **String representation check (`myRules[0].toString() === '[object CSSStyleRule]'`)**: This checks if the string representation of the rule matches a specific format. **Pros and Cons** 1. **Type checking**: Pros - simple, fast, cons - may not work correctly if the `type` property is not what you expect. 2. **Instance checking**: Pros - more robust than type checking, cons - slower due to dynamic typing checks. 3. **String representation check**: Pros - provides additional information about the rule, cons - may require special handling for non-standard rules. **Library and its purpose** The `CSSStyleRule` class is a part of the Web API, which allows JavaScript to manipulate CSS stylesheets on web pages. **Special JS feature or syntax** None mentioned in this benchmark. **Other considerations** * Using `instanceof` can be slower than type checking because it involves dynamic typing checks. * The `toString()` method may return different results for non-standard rules. * The `type` property is not always equal to 1, even if the rule is a `CSSStyleRule`. **Alternatives** Other ways to check if an element is a CSS rule include: * Using a library like `css-select` or `css-tree` to parse the stylesheet and extract the rules. * Creating a custom function that checks for specific characteristics of a CSS rule. Keep in mind that these alternatives may introduce additional complexity, overhead, or dependencies.
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