Benchmark: querySelector(".class") vs getElementsByClassName("class")[0]

HTML Preparation code:

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

Tests:

querySelector
const x = document.querySelector(".test");
getElementsByClassName
const y = 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

Autogenerated LLM Summary (model llama3.2:3b, generated 27 days ago):

LLMs can make mistakes. Check important info.

I'd be happy to explain the JavaScript microbenchmark being tested on MeasureThat.net.

**What's being tested?**

The benchmark tests two ways of selecting an HTML element with a specific class: using `document.querySelector` and `document.getElementsByClassName`. The goal is to determine which method is faster for this particular use case.

**Options compared**

There are only two options being compared:

1. **`document.querySelector(".test")`**: This method uses the CSS selector syntax to select an element by its class name. It returns the first matching element, or `null` if no element matches.
2. **`document.getElementsByClassName("test")[0]`**: This method uses a legacy way of selecting elements by their class name. It returns an array of all matching elements, and we're only interested in the first element (`[0]`).

**Pros and cons**

* **`document.querySelector(".test")`**:
	+ Pros: Modern and efficient way to select elements using CSS selectors.
	+ Cons: May not work as expected if the class name is dynamically added or removed, as it relies on the DOM's current state. Also, older browsers may have issues with this method.
* **`document.getElementsByClassName("test")[0]`**:
	+ Pros: Widely supported by older browsers and works even if the class name is dynamically added or removed.
	+ Cons: Less efficient than `querySelector`, as it requires parsing the entire element list to find the first match.

**Library usage**

Neither of these methods uses a specific library. They are built-in DOM APIs provided by modern web browsers.

**Special JS feature**

This benchmark doesn't use any special JavaScript features or syntax beyond what's required for the test cases. If you're interested in testing more advanced features, MeasureThat.net has a vast range of benchmarks covering various topics.

**Alternatives**

If you're looking for alternative ways to select elements with a class name, some other methods include:

* **`document.querySelectorAll(".test")`**: Returns an array of all matching elements. If you only need the first element, you can use `[0]`, like `document.getElementsByClassName`.
* **`element.classList.contains("test")`**: Checks if an element has a specific class without selecting it. You would then need to select the element using another method.

Keep in mind that these alternatives may have their own trade-offs and usage scenarios. MeasureThat.net's benchmarks are designed to help you compare performance across different browsers, libraries, and techniques.

Latest run results:

Run details: (Test run date: 4 years ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_5) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/13.1.1 Safari/605.1.15

Browser/OS: Safari 13 on Mac OS X 10.15.5

View result in a separate tab

Test name	Executions per second
querySelector	3857881.5 Ops/sec
getElementsByClassName	4128331.0 Ops/sec

Related benchmarks:

querySelector(".class") vs getElementsByClassName("class")[0] (version: 0)

Comparing performance of: querySelector vs getElementsByClassName

Created: 4 years ago by: Guest

Jump to the latest result

querySelector

getElementsByClassName

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 27 days ago):