Benchmark: Performance of query selector vs className

HTML Preparation code:


<div class='test' id='test'></div>

Tests:

querySelector
document.querySelector(".test")
getElementsByClassName
document.getElementsByClassName(".test")

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
querySelector
getElementsByClassName

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: one year ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:109.0) Gecko/20100101 Firefox/115.0

Browser/OS: Firefox 115 on Windows

View result in a separate tab

Test name	Executions per second
querySelector	2755641.2 Ops/sec
getElementsByClassName	5754401.5 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's break down what's being tested in this benchmark.

**What is being tested?**

The provided JSON represents a benchmark that measures the performance of two different methods to select elements in HTML documents: `document.querySelector()` and `document.getElementsByClassName()`. These methods are used to retrieve an element or a list of elements from an HTML document based on their class names, IDs, or tag names.

**Options being compared**

The two options being compared are:

1. **`document.querySelector()`**: This method returns the first element that matches the specified selector. It's a powerful and flexible way to select elements, but it can be slower than other methods if used with complex selectors.
2. **`document.getElementsByClassName()`**: This method returns a live HTMLCollection of all elements with the specified class name. It's generally faster than `querySelector()` for simple class-based selectors.

**Pros and Cons**

* `document.querySelector()`: Pros:
	+ Highly flexible and powerful
	+ Can be used with complex selectors, making it suitable for complex layouts or dynamic content
	+ Can return multiple elements at once
Cons:
	+ May be slower than other methods if used with complex selectors
	+ Requires specifying the exact class name or attribute value
* `document.getElementsByClassName()`: Pros:
	+ Generally faster than `querySelector()` for simple class-based selectors
	+ Returns a live HTMLCollection, allowing for dynamic updates
Cons:
	+ Less flexible and powerful than `querySelector()`
	+ May not work well with complex selectors or dynamic content

**Library**

There is no explicit library mentioned in the benchmark JSON. However, it's worth noting that both `document.querySelector()` and `document.getElementsByClassName()` are part of the DOM (Document Object Model) API, which is a built-in API for interacting with HTML documents.

**Special JS features/syntax**

None of the specific JavaScript features or syntax are mentioned in this benchmark. It only focuses on comparing two different methods for selecting elements.

**Other alternatives**

If you're looking for alternative methods to select elements, here are a few:

1. **`document.querySelectorAll()`**: This method returns a NodeList of all elements that match the specified selector.
2. **`element.querySelector()` / `element.getElementsByClassName()`**: These methods can be used on individual elements (not just documents) to select child or sibling elements.

Keep in mind that these alternatives may have different performance characteristics and use cases compared to `document.querySelector()` and `document.getElementsByClassName()`.

Related benchmarks:

Performance of query selector vs className (version: 0)

Comparing performance of: querySelector vs getElementsByClassName

Created: one year ago by: Guest

Jump to the latest result

querySelector

getElementsByClassName

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

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