Benchmark: querySelector vs getElementsByClassName vs querySelectorAll

HTML Preparation code:

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

Tests:

getElementsByClassName
document.getElementsByClassName(".test")
querySelectorAll
document.querySelectorAll(".test")

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
getElementsByClassName
querySelectorAll

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 25 days ago):

LLMs can make mistakes. Check important info.

Let's dive into the world of JavaScript microbenchmarks and analyze what's being tested on MeasureThat.net.

**Benchmark Overview**

The benchmark compares three ways to select HTML elements from a document: `getElementsByClassName`, `querySelectorAll`, and the DOM API's native query methods (`document.querySelector` and `document.querySelectorAll`). The test is designed to measure the performance of these approaches in various scenarios.

**Options Compared**

The two main options being compared are:

1. **`getElementsByClassName`**: This method returns a collection of elements that match the specified class name.
2. **`querySelectorAll`**: This method returns a NodeList of elements that match the specified CSS selector.

Both methods use different approaches to select elements, which affects their performance characteristics.

**Pros and Cons**

Here's a brief summary of each approach:

* `getElementsByClassName`:
	+ Pros: Simple and widely supported; can be used with CSS class names.
	+ Cons: Returns a collection of elements, which can lead to slower performance due to the need to iterate over the result set. Additionally, this method is not optimized for modern browsers and may use more DOM nodes than necessary.
* `querySelectorAll`:
	+ Pros: More efficient than `getElementsByClassName`, as it uses CSS selectors to select elements directly. This approach can also be used with more complex selectors.
	+ Cons: Requires a valid CSS selector, which can limit its applicability.

**Library and Purpose**

In this benchmark, the browser's DOM API is being compared. The `document` object provides access to various DOM methods, including `getElementsByClassName`, `querySelectorAll`, and others.

**Special JS Feature or Syntax**

None of the tested code snippets use any special JavaScript features or syntax that would require additional explanation.

**Other Alternatives**

If you need to select HTML elements in a different way, here are some alternative approaches:

* Using `document.querySelector` (one-time selector): This method returns the first element that matches the specified CSS selector. If multiple elements match, it returns only the first one.
* Using `document.querySelectorAll` (multiple-time selector): Similar to `querySelector`, but returns all matching elements in a NodeList.

Keep in mind that these alternatives may have different performance characteristics than `getElementsByClassName` and `querySelectorAll`.

**Benchmark Preparation Code**

The provided HTML preparation code creates three identical `<div>` elements with the class `test`. The script preparation code is empty, which means no additional JavaScript code is executed before running the benchmark.

By analyzing this benchmark, you can gain insights into the performance characteristics of different methods for selecting HTML elements in a web application.

Latest run results:

Run details: (Test run date: 5 years ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.98 Safari/537.36

Browser/OS: Chrome 71 on Windows

View result in a separate tab

Test name	Executions per second
getElementsByClassName	3134319.2 Ops/sec
querySelectorAll	782991.9 Ops/sec

Related benchmarks:

querySelector vs getElementsByClassName vs querySelectorAll (version: 0)

Comparing performance of: getElementsByClassName vs querySelectorAll

Created: 5 years ago by: Guest

Jump to the latest result

getElementsByClassName

querySelectorAll

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 25 days ago):