Benchmark: getElementsByClassName()[0] vs querySelectorAll

HTML Preparation code:

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

Tests:

By Class Name
document.getElementsByClassName('test')[0];
Query Selector
document.querySelector('.test');

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
By Class Name
Query Selector

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 9 months ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:141.0) Gecko/20100101 Firefox/141.0

Browser/OS: Firefox 141 on Windows

View result in a separate tab

Test name	Executions per second
By Class Name	2068744.6 Ops/sec
Query Selector	2096478.6 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's break down what's being tested in the provided JSON.

**Benchmark Definition**

The website is comparing two approaches to select an HTML element: `document.getElementsByClassName('test')[0]` (By Class Name) and `document.querySelector('.test')` (Query Selector).

**Options Compared**

There are two options being compared:

1. **By Class Name**: This method uses the `getElementsByClassName()` method, which returns a live HTMLCollection of elements with the specified class name. The `[0]` index is used to access the first element in the collection.
2. **Query Selector**: This method uses the `querySelector()` method, which returns the first element that matches the specified CSS selector.

**Pros and Cons**

**By Class Name:**

Pros:

* Wide browser support (not specific to CSS selectors)
* Can be more flexible for complex class names

Cons:

* May return multiple elements if there are multiple elements with the same class name
* Can be slower due to the live collection nature of `getElementsByClassName()`

Query Selector:

Pros:

* More precise and efficient, returning only the first matching element
* Uses CSS selectors, which can be more concise and expressive

Cons:

* Requires support for CSS selectors in the browser (not all browsers support this)
* Can be slower due to the parsing of CSS selectors

**Other Considerations**

Both methods have limitations. The `getElementsByClassName()` method may return a live collection, which means that if you modify the DOM after calling `getElementsByClassName()`, it will still return the same elements on subsequent calls. In contrast, `querySelector()` returns a static value and does not pollute the DOM.

**Library Usage**

The benchmark uses the `document` object, which is part of the DOM (Document Object Model) API. The `document` object provides access to various properties and methods that allow you to interact with an HTML document.

**Special JS Features/Syntax**

There are no specific JavaScript features or syntax being tested in this benchmark.

**Other Alternatives**

If you want to measure the performance of different CSS selector algorithms, you could consider adding more test cases, such as:

* Using `querySelectorAll()` instead of `querySelector()`
* Using different class names or element IDs for comparison
* Adding more complex CSS selectors (e.g., `>`, `~`, `[attribute]`) to the benchmark

Keep in mind that each additional test case can increase the complexity and scope of the benchmark, which may affect its accuracy.

Related benchmarks:

getElementsByClassName()[0] vs querySelectorAll (version: 0)

Comparing performance of: By Class Name vs Query Selector

Created: 5 years ago by: Guest

Jump to the latest result

By Class Name

Query Selector

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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