Benchmark: querySelector vs getElementsByClassName access

HTML Preparation code:

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

Tests:

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

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

LLMs can make mistakes. Check important info.

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

**Benchmark Definition**

The benchmark is designed to compare the performance of two methods for selecting an HTML element: `querySelector` and `getElementsByClassName`. The benchmark is focused on accessing elements by class name, specifically `.test`.

**Options Compared**

Two options are compared:

1. **`document.querySelector(".test")`**: This method uses a CSS selector to find the first element with the class `test`. It's a modern approach that uses the W3C CSS selectors API.
2. **`document.getElementsByClassName("test")[0]`**: This method returns an array of elements with the class `test`, and then selects the first element from this array using `[0]`.

**Pros and Cons**

**`querySelector`:**

Pros:

* More efficient and modern approach, especially for complex selectors.
* Less memory usage since it only retrieves a single element.

Cons:

* Requires support for W3C CSS selectors API, which might not be enabled in all browsers.
* May have slightly higher overhead due to the more complex parsing process.

**`getElementsByClassName`:**

Pros:

* Widely supported across older browsers that don't support `querySelector`.
* Can return an array of elements if there are multiple elements with the same class name.

Cons:

* More memory usage since it returns a full array of matching elements.
* Can be slower for large numbers of elements due to the need to parse the entire array.

**Library and Purpose**

The `Document` object, specifically its `querySelector` and `getElementsByClassName` methods, are part of the DOM (Document Object Model) API. These methods allow you to interact with HTML documents programmatically.

**Special JavaScript Feature/Syntax**

There is no special JavaScript feature or syntax used in this benchmark beyond what's typically available in modern browsers. However, it's worth noting that the `querySelector` method relies on CSS selectors, which can be complex and powerful but also require careful use to avoid performance issues.

**Other Alternatives**

If you need a more detailed comparison, other alternatives could include:

* Using `document.querySelectorAll(".test")` (which returns a NodeList) vs. `getElementsByClassName("test")`.
* Comparing the performance of using `querySelectorAll` with or without specific selectors.
* Evaluating the impact of disabling CSS caching on query selector performance.

Keep in mind that benchmarking JavaScript performance can be complex, and results may vary depending on the specific use case and browser environment.

Latest run results:

Run details: (Test run date: 3 years ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/94.0.4606.61 Safari/537.36

Browser/OS: Chrome 94 on Windows

View result in a separate tab

Test name	Executions per second
querySelector	3369102.2 Ops/sec
getElementsByClassName	3326268.8 Ops/sec

Related benchmarks:

querySelector vs getElementsByClassName access (version: 0)

Comparing performance of: querySelector vs getElementsByClassName

Created: 3 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 one month ago):