Benchmark: querySelector() vs getElementsByClassName()[0]

HTML Preparation code:

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

Tests:

querySelector
document.querySelector(".test");
getElementsByClassName
document.getElementsByClassName("test")[0];

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
querySelector
getElementsByClassName

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 14 days ago)

User agent: Mozilla/5.0 (X11; Linux x86_64; rv:149.0) Gecko/20100101 Firefox/149.0

Browser/OS: Firefox 149 on Linux

View result in a separate tab

Test name	Executions per second
querySelector	718869.9 Ops/sec
getElementsByClassName	2436389.2 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's dive into the world of MeasureThat.net and explore what's being tested in this specific benchmark.

**What is being tested?**

The provided JSON represents a JavaScript microbenchmark that compares two DOM query methods: `document.querySelector()` and `document.getElementsByClassName()[0]`. The benchmark aims to measure which method is faster and more efficient for selecting an element by its class name.

**Options compared:**

Two options are being compared:

1. `document.querySelector(".test")`: This method selects the first element in the DOM tree that matches the specified CSS selector (in this case, `.test`).
2. `document.getElementsByClassName("test")[0]`: This method retrieves an array of all elements in the DOM tree that match the specified class name (`"test"`), and then returns the first element from that array.

**Pros and Cons:**

* **`document.querySelector(".test")`:**
	+ Pros:
		- More efficient, as it only needs to traverse a single element from the DOM tree.
		- Can be more selective in terms of CSS selectors, allowing for finer-grained selection.
	+ Cons:
		- May not work if the element is dynamically generated or has multiple matches.
* **`document.getElementsByClassName("test")[0]`:**
	+ Pros:
		- Works even if there are multiple elements with the same class name.
	+ Cons:
		- Requires iterating over all matching elements to get the first one, which can be slower for large datasets.

**Library and purpose:**

There is no specific library mentioned in this benchmark. The methods being compared are part of the native DOM API provided by web browsers.

**Special JS features or syntax:**

None are explicitly used in this benchmark.

**Alternative approaches:**

Other alternatives to compare could include:

* Using `document.querySelector` with a more complex CSS selector (e.g., `.test > span`) to see if it outperforms the simple class name query.
* Adding additional elements with different classes and using `getElementsByClassName` to see how its performance scales with multiple matches.
* Comparing `querySelector` and `getElementsByClassName` against other libraries or frameworks that provide similar functionality (e.g., jQuery).

Keep in mind that these alternatives would require modifying the benchmark JSON and adding new test cases.

Related benchmarks:

querySelector() vs getElementsByClassName()[0] (version: 0)

Comparing performance of: querySelector vs getElementsByClassName

Created: 7 years ago by: Guest

Jump to the latest result

querySelector

getElementsByClassName

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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