Benchmark: getElementByClassName vs querySelector

HTML Preparation code:

<div class="my-id"></div>

Tests:

querySelector
document.querySelector(".my-class")
getElementById
document.getElementsByClassName("my-class")[0]

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
querySelector
getElementById

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 2 months ago)

User agent: Mozilla/5.0 (X11; Linux x86_64; rv:128.0) Gecko/20100101 Goanna/6.8 PaleMoon/34.0.1

Browser/OS: Pale Moon (Firefox Variant) 34 on Linux

View result in a separate tab

Test name	Executions per second
querySelector	2790424.8 Ops/sec
getElementById	6069149.0 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's break down the benchmark and explain what's being tested.

**What is being tested?**

The benchmark is comparing two ways to select elements in HTML documents:

1. `document.querySelector(".my-class")`
2. `document.getElementsByClassName("my-class")[0]`

In other words, we're measuring the performance of two different approaches to find an element with a specific class name.

**Options compared:**

The two options being compared are:

* `querySelector`: a method that returns the first element matching the specified CSS selector.
* `getElementByClassName`: not a standard JavaScript method (I'll explain why later), but rather a hypothetical function that might be used to achieve similar results as `querySelector`.

**Pros and cons of each approach:**

1. **`querySelector`:**
	* Pros:
		+ More efficient, as it uses the CSS selector engine, which is optimized for performance.
		+ Returns the first matching element, making it suitable for single-element selections.
	* Cons:
		+ May not be as fast as `getElementByClassName` if used with a complex selector or multiple elements.
2. **`getElementByClassName` (hypothetical):**
	* Pros:
		+ Might be faster than `querySelector` in certain scenarios, especially for simpler selectors or single-element selections.
	* Cons:
		+ Not a standard JavaScript method, making it less reliable and more prone to browser inconsistencies.

**Library used:**

There is no library being explicitly referenced in the benchmark definition. However, if we consider `querySelector` as a part of the DOM API (Document Object Model), it's likely using the CSS selector engine provided by the browser.

**Special JS feature or syntax:**

The benchmark doesn't use any special JavaScript features or syntax that I'm aware of. It seems to be focusing on the basic query methods for selecting elements in HTML documents.

Now, let's discuss some alternative approaches:

1. **`getElementsByClassName`**: This is another method that returns a collection of all elements with the specified class name. While it's not being tested directly here, it's an alternative way to achieve similar results as `querySelector`.
2. **CSS selectors in JavaScript libraries**: Some JavaScript libraries, like jQuery, provide their own CSS selector engine for selecting elements. These libraries might offer more advanced features and optimizations than native browser implementations.
3. **DOM traversal methods**: Instead of using query methods, you can use DOM traversal methods like `document.body.querySelectorAll()` to select elements.

Keep in mind that these alternatives may have different performance characteristics, depending on the specific library or implementation used.

Overall, this benchmark provides a simple and focused comparison between two common ways to select elements in HTML documents.

Related benchmarks:

getElementByClassName vs querySelector (version: 0)

Comparing performance of: querySelector vs getElementById

Created: 7 years ago by: Guest

Jump to the latest result

querySelector

getElementById

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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