Benchmark: querySelector vs. getElementsByClassName nested dom

HTML Preparation code:

<div>
    <div>
        <div>
            <div>
            </div>
        </div>
        <div>
            <div class="test">
            </div>
        </div>
        <div>
            <div>
            </div>
        </div>
        <div>
            <div class="test">
            </div>
        </div>
        <div>
            <div>
            </div>
        </div>
        <div>
            <div class="test">
            </div>
        </div>
        <div>
            <div>
            </div>
        </div>
    </div>
</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: 8 months ago)

User agent: Mozilla/5.0 (Linux; Android 10; K) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/124.0.0.0 Mobile Safari/537.36

Browser/OS: Chrome Mobile 124 on Android

View result in a separate tab

Test name	Executions per second
querySelector	2194322.2 Ops/sec
getElementsByClassName	2061792.9 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's dive into the world of JavaScript microbenchmarks.

**Benchmark Overview**

The provided benchmark measures the performance difference between `document.querySelector` and `document.getElementsByClassName` when used to select an element with a specific class (`"test"`). The test case creates a nested DOM structure with multiple target nodes, ensuring that both querySelector and getElementsByClassName must traverse the DOM to find the desired element.

**Options Compared**

Two options are being compared:

1. **querySelector**: This method uses a CSS selector to select the first element matching the specified criteria. It's generally more efficient than using `getElementsByClassName` because it only traverses the DOM once and can stop early if no match is found.
2. **getElementsByClassName**: This method returns a live HTMLCollection of all elements that have the specified class name. It requires traversing the entire DOM to find the first matching element.

**Pros and Cons**

**querySelector:**

Pros:

* Efficient: Only traverses the DOM once, making it faster for large DOMs.
* Stop early: If no match is found, it immediately returns null or undefined.

Cons:

* More complex: Requires a CSS selector syntax that can be harder to read and write.
* Browser support: While widely supported, older browsers might not have optimal implementation.

**getElementsByClassName:**

Pros:

* Simpler: Uses a straightforward method to select elements based on class names.
* Better browser support: Most modern browsers have excellent support for this method.

Cons:

* Less efficient: Requires traversing the entire DOM to find the first matching element, making it slower for large DOMs.

**Library Usage**

In the provided benchmark definition JSON, the `document` object is used as a library. The `document` object provides various methods and properties for interacting with the Document Object Model (DOM), which allows JavaScript code to manipulate HTML documents.

**Special JS Feature/Syntax**

There are no special JavaScript features or syntaxes being tested in this benchmark. Both querySelector and getElementsByClassName use standard JavaScript DOM API methods.

**Other Considerations**

* **Performance Impact**: The performance difference between these two methods can be significant for large-scale web applications.
* **DOM Manipulation**: This benchmark assumes that the DOM is already populated with data, which may not always be the case. You might need to consider benchmarks for empty or partially populated DOMs.

**Alternatives**

If you're interested in exploring alternative JavaScript libraries or frameworks for DOM manipulation and query selection, some popular options include:

* **QueryList**: A lightweight library that provides a simple API for querying the DOM.
* **Zepto**: A fast and feature-rich DOM manipulation library.
* **jQuery**: A widely used JavaScript library that includes powerful DOM manipulation and query methods.

These alternatives might offer performance benefits or more intuitive APIs, but they may also introduce additional dependencies and complexity.

Related benchmarks:

querySelector vs. getElementsByClassName nested dom (version: 0)

Testing querySelector against getElementsByClassName in a larger DOM with multiple target nodes (only one is needed)

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 2 months ago):