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

Test name	Executions per second
querySelector	5316135.5 Ops/sec
getElementsByClassName (first element of)	3526761.8 Ops/sec
getElementById	4539970.0 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 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.

Related benchmarks:

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

Jump 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):