Benchmark: querySelector vs getElementsByClassName (get first element)

HTML Preparation code:

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

Tests:

querySelector
document.querySelector(".test")
getElementsByClassName (first element of)
document.getElementsByClassName(".test")[0]
getElementById
document.getElementById("test")

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
querySelector
getElementsByClassName (first element of)
getElementById

Fastest: N/A

Slowest: N/A

Latest run results:

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

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/122.0.0.0 Safari/537.36 Edg/122.0.0.0

Browser/OS: Chrome 122 on Windows

View result in a separate tab

querySelector

5.3M/s

getElementById

4.5M/s

getElementsByClassName (first element of)

3.5M/s

View exact numbers

Test name	Executions per second
✓ querySelector	5,316,136 Ops/sec
getElementById	4,539,970 Ops/sec
getElementsByClassName (first element of)	3,526,762 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 provided JSON and explain what's being tested, compared, and the pros/cons of different approaches.

**What is being tested?**

The benchmark measures the performance difference between three DOM selection methods:

1. `document.querySelector(".test")`
2. `document.getElementsByClassName("test")[0]` (note: this method returns an array, but we're only interested in the first element)
3. `document.getElementById("test")`

**What options are compared?**

The benchmark compares the performance of these three DOM selection methods:

1. **`querySelector`**: a CSS selector-based method that selects elements by their class, ID, or attributes.
2. **`getElementsByClassName (first element of)`**: a method that returns an array of elements with the specified class name and returns only the first element.
3. **`getElementById`**: a method that returns a single element with the specified ID.

**Pros and Cons:**

1. **`querySelector`**:
	* Pros:
		+ Fast, especially for complex selections (e.g., `.test > .sub`)
		+ Can handle multiple elements at once
	* Cons:
		+ May not work as expected if there are multiple elements with the same class or ID
		+ Can be slower for simple selections (e.g., `document.querySelector(".test")` without any additional criteria)
2. **`getElementsByClassName (first element of)`**:
	* Pros:
		+ Guarantees to return only the first matching element, which can improve performance in certain scenarios
	* Cons:
		+ Returns an array, even if there's only one element, which requires more work to process
		+ May be slower due to the overhead of creating and iterating over the array
3. **`getElementById`**:
	* Pros:
		+ Fast and efficient for single-element selections (e.g., `document.getElementById("test")`)
	* Cons:
		+ Limited to only selecting by ID, which may not be suitable for all use cases

**Library and its purpose:**

None of the provided test cases rely on any external libraries.

**Special JS feature or syntax:**

There's no special JavaScript feature or syntax used in these benchmarks. The code is straightforward and uses basic DOM manipulation methods.

**Other alternatives:**

If you're interested in exploring alternative approaches, consider the following:

1. **`querySelectorAll`**: similar to `querySelector`, but returns an array of all matching elements.
2. **`getElementsByClassName`**: another method that returns an array of elements with the specified class name (not as widely supported as `getElementsByClassName`).
3. **`getElementById` alternatives**, such as using `document.querySelector` with the `id` attribute instead of a class or ID.

Keep in mind that these alternative methods may have different performance characteristics, and it's essential to test them specifically for your use case.

querySelector vs getElementsByClassName (get first element) (version: 0)

Comparing performance of: `querySelector vs getElementsByClassName (first element of) vs getElementById`

Created: 7 years ago by: Guest

Go to the latest result

querySelector

getElementsByClassName (first element of)

getElementById

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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

querySelector vs getElementsByClassName (get first element) (version: 0)

Comparing performance of: querySelector vs getElementsByClassName (first element of) vs getElementById

Created: 7 years ago by: Guest

Go to the latest result

querySelector

getElementsByClassName (first element of)

getElementById

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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

Related benchmarks

Comparing performance of: `querySelector vs getElementsByClassName (first element of) vs getElementById`