Benchmark: selector test - MeasureThat.net

HTML Preparation code:

<section><div class="basic"></div></section>

Tests:

querySelector
document.querySelector('section:first-child .basic');
getElementsByTagName
document.getElementsByTagName('section').item(0).getElementsByClassName('.basic').item(0)

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
querySelector
getElementsByTagName

Fastest: N/A

Slowest: N/A

Latest 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 the provided JSON data and explain what's being tested.

**Benchmark Definition**

The `BenchmarkDefinition` json represents a JavaScript microbenchmark that tests two different approaches to select an HTML element:

1. `document.querySelector('section:first-child .basic')`
2. `document.getElementsByTagName('section').item(0).getElementsByClassName('.basic').item(0)`

Both expressions aim to select the first `<div>` element with class `basic` inside a `<section>` element, but they use different methods and syntax.

**Options Compared**

The two options are compared in terms of performance. The goal is to determine which approach is faster and more efficient.

**Pros and Cons**

1. **`document.querySelector('section:first-child .basic')`**
	* Pros:
		+ More concise and readable syntax.
		+ Reduces the number of DOM operations, making it potentially faster.
	* Cons:
		+ Requires support for CSS selectors in JavaScript (introduced in ECMAScript 5).
		+ May not work as expected if the first `<section>` element is not a child of the root document.
2. **`document.getElementsByTagName('section').item(0).getElementsByClassName('.basic').item(0)`** (also known as "Sizzle" or "CSS Selectors")
	* Pros:
		+ Works in older browsers that don't support CSS selectors in JavaScript.
		+ Provides a fallback mechanism for cases where the first `<section>` element is not a child of the root document.
	* Cons:
		+ More verbose and less readable syntax.
		+ Invokes multiple DOM operations, which can be slower.

**Library Usage**

In this benchmark, Sizzle (also known as "CSS Selectors") is used. Sizzle is a library that provides an implementation of CSS selectors for JavaScript engines. It allows developers to select elements using a syntax similar to CSS, making it easier to write flexible and efficient code.

**Special JS Feature/Syntax**

The benchmark uses the `querySelector` method, which was introduced in ECMAScript 5 (ES5) as part of the HTML5 specification. This method is supported by most modern browsers, but older browsers may not have native support for it.

**Alternatives**

Other alternatives to these two approaches include:

* Using `document.querySelector` with a different CSS selector (e.g., `document.querySelector('div.basic')`)
* Using a library like Sizzle or other CSS selectors implementations
* Implementing a custom selector function using JavaScript

Keep in mind that the performance difference between these approaches may vary depending on the specific use case, browser version, and hardware configuration.

Related benchmarks:

selector test (version: 0)

Comparing performance of: querySelector vs getElementsByTagName

Created: 7 years ago by: Guest

Jump to the latest result

querySelector

getElementsByTagName

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):