Benchmark: QuerySelector vs getElementsByClassName - Emo test

HTML Preparation code:

<div class="test"></div>

Tests:

query
document.querySelector('.test')
getElementsByClassName
document.getElementsByClassName('test')[0]

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
query
getElementsByClassName

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 27 days ago):

LLMs can make mistakes. Check important info.

Let's break down the provided benchmark and explain what's being tested, compared, and discussed.

**What is being tested?**

The benchmark tests two different ways to select an element from an HTML document: `document.querySelector` (query) and `document.getElementsByClassName` (getElementsByClassName). The test case uses a simple HTML element with a class name "test".

**Options being compared**

There are two options being compared:

1. **`document.querySelector('.test')`**: This method is used to select an element by its class name.
2. **`document.getElementsByClassName('test')[0]`**: This method is also used to select an element by its class name, but it returns a NodeList of all elements with the specified class name, and then uses `[0]` to get the first element in the list.

**Pros and Cons**

* `document.querySelector('.test')`:
	+ Pros: More efficient and concise way to select an element by its class name. It's also more modern and widely supported.
	+ Cons: If no elements are found, it returns null. If you need to get all elements with the specified class name, you need to use a different method or iterate over the results.
* `document.getElementsByClassName('test')[0]`:
	+ Pros: Returns an element even if none is found in the DOM. However, this can be slower and less efficient than using `querySelector`.
	+ Cons: The syntax can look more verbose, and it's not as modern as `querySelector`.

**Library and purpose**

There isn't a specific library being used here.

**Special JS feature or syntax**

This benchmark doesn't use any special JavaScript features or syntax. It only uses the standard DOM API methods for selecting elements.

**Other alternatives**

If you wanted to compare other methods, some alternative approaches could be:

* Using `document.querySelectorAll('.test')` instead of `getElementsByClassName`. This would return a NodeList of all elements with the specified class name.
* Using `element.matches()` or `element.contains()` to check if an element matches a selector.

**Benchmark preparation code**

The benchmark preparation code is a simple HTML element with a class name "test": `<div class="test"></div>`. This ensures that both methods can select the same element.

In summary, this benchmark tests two common ways to select an element by its class name in JavaScript: `document.querySelector` and `document.getElementsByClassName`. The results show that `querySelector` is more efficient but returns null if no elements are found.

Latest run results:

Run details: (Test run date: 4 years ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/78.0.3904.108 Safari/537.36

Browser/OS: Chrome 78 on Windows

View result in a separate tab

Test name	Executions per second
query	2458576.8 Ops/sec
getElementsByClassName	2521805.5 Ops/sec

Related benchmarks:

QuerySelector vs getElementsByClassName - Emo test (version: 0)

Comparing performance of: query vs getElementsByClassName

Created: 4 years ago by: Guest

Jump to the latest result

query

getElementsByClassName

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 27 days ago):