Benchmark: querySelector vs getElementsByClassName test

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: 6 years ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/67.0.3396.99 Safari/537.36

Browser/OS: Chrome 67 on Windows

View result in a separate tab

Test name	Executions per second
querySelector	1286404.4 Ops/sec
getElementsByClassName	1230119.8 Ops/sec

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

LLMs can make mistakes. Check important info.

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

**What is being tested?**

The benchmark compares two methods to select an HTML element with a specific class: `querySelector` and `getElementsByClassName`. The test case creates a simple HTML document with a single `<div>` element containing the text "test" and classes `test` and `class1`.

**Options compared:**

1. `querySelector`: A method that selects elements based on a CSS selector. In this case, it's used to select the first `<div>` element that matches the `.test` class.
2. `getElementsByClassName`: A method that returns a list of all elements with the specified class name.

**Pros and Cons:**

* **querySelector**: Pros:
	+ More efficient in terms of performance, especially for complex selectors.
	+ Can be more flexible and powerful when used with CSS selectors.
* Cons:
	+ May not work as expected if the element is not found (returns `null` by default).
	+ Limited to selecting elements based on their class names or attributes.
* `getElementsByClassName`: Pros:
	+ Returns all matching elements, even if there are multiple elements with the same class name.
	+ Works even if the element is not found.
* Cons:
	+ Can be slower and less efficient than `querySelector` for large datasets.
	+ May return more results than needed.

**Other considerations:**

* Both methods have a limit on the number of matching elements that can be returned. For `querySelector`, this limit is 24, while for `getElementsByClassName`, it's 1000 (although this value may vary depending on the browser and platform).
* The benchmark does not consider other factors like element accessibility or attribute selectors.

**Libraries and special features:**

In this benchmark, there are no libraries used. However, if a library were used to extend or modify the behavior of `querySelector` or `getElementsByClassName`, it could potentially impact performance or functionality.

**Special JavaScript features:**

There is no mention of any special JavaScript features or syntax in the provided benchmark code.

**Alternatives:**

If you want to compare other methods for selecting elements, here are some alternatives:

* `querySelectorAll`: Similar to `querySelector`, but returns a NodeList containing all matching elements instead of just one.
* `querySelectorAll` with a CSS selector: Can be used to select multiple elements based on a single CSS selector.
* `getElementsByTagName`: Returns an HTMLCollection of all elements with the specified tag name.

Related benchmarks:

querySelector vs getElementsByClassName test (version: 0)

Comparing performance of: querySelector vs getElementsByClassName

Created: 6 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 2 months ago):