Benchmark: Testing querySelectorAll vs getElementsByClassName

HTML Preparation code:

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

Tests:

querySelectorAll
document.querySelectorAll(".test")
getElementsByClassName
document.getElementsByClassName(".test")

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
querySelectorAll
getElementsByClassName

Fastest: N/A

Slowest: N/A

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/93.0.4577.82 Safari/537.36

Browser/OS: Chrome 93 on Windows

View result in a separate tab

Test name	Executions per second
querySelectorAll	830634.9 Ops/sec
getElementsByClassName	3020150.0 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.

**Benchmark Overview**

The benchmark is designed to compare two methods for selecting elements in an HTML document: `document.querySelectorAll()` and `document.getElementsByClassName()`. The test creates a simple HTML element with a class name "test" and then uses these two methods to select that element from the DOM.

**Options Compared**

Two options are being compared:

1. **`document.querySelectorAll('.test')`**: This method returns a NodeList of all elements in the document that have the class "test". The NodeList is a collection of elements, not a single element, so it can be faster to iterate over it.
2. **`document.getElementsByClassName('test')`**: This method also returns a NodeList of elements with the class "test", but it's specific to HTML elements (not attributes or pseudo-classes). The NodeList returned by this method is not as flexible as the one from `querySelectorAll()`.

**Pros and Cons**

*   **`document.querySelectorAll('.test')`**
    *   Pros:
        *   Returns a NodeList that includes all elements, regardless of their type (HTML or attribute selectors).
        *   Can be more efficient for complex selections.
    *   Cons:
        *   May return more elements than needed, which can lead to performance issues if not handled correctly.
*   **`document.getElementsByClassName('test')`**
    *   Pros:
        *   Returns a NodeList specific to HTML elements with the class "test".
        *   Can be faster for simple selections of only HTML elements.
    *   Cons:
        *   May return fewer elements than needed, which can lead to performance issues if not handled correctly.

**Library Usage**

There is no explicit library mentioned in the benchmark. However, both methods rely on the DOM API, which is a built-in part of JavaScript and is used extensively throughout web development.

**Special JS Feature or Syntax**

There are no special features or syntaxes being used beyond standard JavaScript and the DOM API.

**Alternative Approaches**

Other approaches to selecting elements in HTML documents include:

*   **CSS Selectors**: You can use CSS selectors to select elements directly, which can be faster than using the DOM API.
*   **QuerySelector** (and its variants): Some modern browsers support a `querySelector` method that's similar to `querySelectorAll()`, but more efficient for simple selections.

Here is some sample code illustrating these alternative approaches:

```javascript
// CSS Selectors
const element = document.querySelector('.test');

// QuerySelector
const element2 = document.querySelector('.test');
```

Note: These alternatives may have different browser support and may not work in all situations.

Overall, the benchmark provides a good starting point for understanding the performance differences between these two common DOM selection methods.

Related benchmarks:

Testing querySelectorAll vs getElementsByClassName (version: 0)

Comparing performance of: querySelectorAll vs getElementsByClassName

Created: 3 years ago by: Guest

Jump to the latest result

querySelectorAll

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):