Benchmark: queryselector vs getElementByClassName

HTML Preparation code:

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

Tests:

querySelector
document.querySelector(".test")
getElementByClassName
document.getElementsByClassName("test")[0]

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
querySelector
getElementByClassName

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 2 years ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/102.0.5005.61 Safari/537.36

Browser/OS: Chrome 102 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
querySelector	4046341.0 Ops/sec
getElementByClassName	3027163.2 Ops/sec

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

LLMs can make mistakes. Check important info.

Measuring performance differences between two approaches is crucial in software development, and measuring performance of querySelector vs getElementByClassName can be particularly interesting.

**What are we testing?**

We are testing the performance of two different methods to select elements from an HTML document:

1. `document.querySelector(" .test")`
2. `document.getElementsByClassName( "test" )[0]`

Both methods aim to retrieve all elements with a class of `test` and return the first matching element.

**Options being compared**

The options being compared are:

* `querySelector`: a method introduced in HTML5, which allows selecting elements by their CSS selectors.
* `getElementByClassName`: an older method that uses the `getElementsByClassName()` function to retrieve all elements with a specific class name and returns them as a list of HTMLElements.

**Pros and Cons**

Here's a brief summary of each approach:

* **querySelector**
	+ Pros:
		- More efficient, since it only retrieves one element at a time, rather than fetching the entire list.
		- Often faster, since it doesn't require creating an array of elements to process.
		- More flexible and powerful for complex queries.
	+ Cons:
		- May be slower if the browser needs to parse and execute multiple CSS selectors.
* **getElementByClassName**
	+ Pros:
		- Simpler and more straightforward than `querySelector`.
		- Can be faster if the element is found quickly, as it only requires a single DOM lookup.
	+ Cons:
		- Inefficient for large sets of matching elements or complex class names.
		- Returns all matching elements in an array, which can lead to slower performance due to the overhead of creating and processing arrays.

**Library and purpose**

Neither `querySelector` nor `getElementByClassName` uses a specific library. Instead, they are built-in methods of the DOM (Document Object Model) API in JavaScript. The `querySelector()` method is implemented as part of the HTML5 standard, while `getElementsByClassName()` has been available since IE8.

**Special JS feature or syntax**

Neither test case uses any special JavaScript features or syntax. They simply utilize the built-in methods mentioned above to compare their performance.

**Other alternatives**

If you need even more flexibility in your querySelector approach, you can use the `querySelectorAll()` method, which returns a NodeList containing all matching elements:

`document.querySelectorAll(".test")`

Alternatively, you can use other CSS selectors or methods like `getElementsByTagName()`, `getElementsById()`, or custom methods implemented by your own JavaScript code.

In general, when choosing between these approaches, consider factors such as the complexity of your queries, the size of your data sets, and your target audience's browser support requirements.

Related benchmarks:

queryselector vs getElementByClassName (version: 0)

Comparing performance of: querySelector vs getElementByClassName

Created: 5 years ago by: Guest

Jump to the latest result

querySelector

getElementByClassName

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):