Benchmark: getElementsByClassName vs querySelector

HTML Preparation code:

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

Tests:

getElementsByClassName
document.getElementsByClassName('test')[0]
querySelector
document.querySelector('.test')

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
getElementsByClassName
querySelector

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 5 years ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/75.0.3770.100 Safari/537.36

Browser/OS: Chrome 75 on Windows

View result in a separate tab

Test name	Executions per second
getElementsByClassName	2748599.2 Ops/sec
querySelector	2783299.5 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 JSON benchmark data and explain what's being tested.

**What is being tested?**

The benchmark compares two approaches to select an HTML element with a class name:

1. `getElementsByClassName`: This method returns an array of all elements that have the specified value as their class attribute.
2. `querySelector`: This method returns the first element that matches the specified CSS selector.

**Options compared:**

* `getElementsByClassName` vs `querySelector`

**Pros and Cons of each approach:**

* **`getElementsByClassName`**:
	+ Pros: More compatible with older browsers (IE8+) since it doesn't rely on CSS selectors. It's also more straightforward to implement.
	+ Cons: Returns an array, which can be slower for single-element selection. The `length` property of the returned array is accessed, which can incur additional overhead.
* **`querySelector`**:
	+ Pros: More efficient and modern approach that takes advantage of CSS selectors. It's also more suitable for selecting elements based on complex conditions.
	+ Cons: Less compatible with older browsers (IE8-) since it relies on CSS selectors.

**Library/Technology used in test case:**

* `querySelector` uses the W3C DOM Query API, which is supported by most modern browsers.

**Special JS feature/syntax:**

None mentioned explicitly. However, it's worth noting that both methods rely on the `document` object, which is a fundamental part of JavaScript DOM interaction.

**Other alternatives:**

* For more complex CSS selectors or attribute selections, other methods like `querySelectorAll()` (similar to `getElementsByClassName`, but returns all matching elements) or `querySelector `[attribute]` might be used.
* For older browsers that don't support CSS selectors, alternative approaches like using `style` attributes or `innerHTML` manipulation might be employed.

In summary, this benchmark compares the performance of two widely used methods for selecting an HTML element based on class names. The `getElementsByClassName` approach is more compatible with older browsers, while the `querySelector` method takes advantage of CSS selectors for a more efficient and modern solution.

Related benchmarks:

getElementsByClassName vs querySelector (version: 0)

Comparing performance of: getElementsByClassName vs querySelector

Created: 5 years ago by: Guest

Jump to the latest result

getElementsByClassName

querySelector

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):