Benchmark: querySelectorAll - vs - getElementsByClassName

HTML Preparation code:

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

Tests:

getElementsByClassName
var foo = document.getElementsByClassName('test') for (var i = 0; i < foo.length; i++) foo[i].dataset.bar
querySelectorAll
var foo = document.querySelectorAll('.test') for (var i = 0; i < foo.length; i++) foo[i].dataset.bar

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
getElementsByClassName
querySelectorAll

Fastest: N/A

Slowest: N/A

Latest run results:

No previous run results

This benchmark does not have any results yet. Be the first one to run it!

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

LLMs can make mistakes. Check important info.

Let's break down the provided benchmark and explain what is being tested.

**What is being tested:**

The benchmark compares two methods for selecting HTML elements in JavaScript:

1. `getElementsByClassName`
2. `querySelectorAll`

Both methods are used to select elements based on their class names. However, they differ in how they handle the selection process.

**Options compared:**

The two options being compared are:

A) Using `getElementsByClassName` method, which returns a live HTMLCollection (a collection of nodes that can be iterated over).
B) Using `querySelectorAll` method, which returns a NodeList (a collection of nodes that can be iterated over).

**Pros and Cons:**

**GetElementsByClassName:**

Pros:

* It is supported by older browsers.
* It allows for more fine-grained control over the selection process.

Cons:

* It can be slower than `querySelectorAll` because it requires iterating over the entire HTMLCollection to find the matching elements.
* It returns a live collection, which means that if you modify the DOM after calling this method, you may get unexpected results.

**querySelectorAll:**

Pros:

* It is generally faster than `getElementsByClassName`.
* It returns a NodeList, which is more efficient and safer to work with in modern browsers.

Cons:

* It is not supported by older browsers.
* It requires using the `MatchesSelector` API (introduced in ECMAScript 2017), which may be considered slower than traditional DOM methods.

**Other considerations:**

When choosing between these two methods, consider the following factors:

* Browser support: If you need to support older browsers, use `getElementsByClassName`. Otherwise, `querySelectorAll` is a better choice.
* Performance: If speed is critical, use `querySelectorAll`.
* DOM modifications: Avoid modifying the DOM after calling either method if you want to ensure consistent results.

**Library or special JavaScript feature:**

Neither of these methods relies on a specific library or special JavaScript feature. They are built-in DOM methods that have been part of the JavaScript language since its inception.

**Other alternatives:**

If you need alternative methods for selecting elements, consider using:

* `document.querySelector` (introduced in ECMAScript 2017): This method is similar to `querySelectorAll`, but it returns a single element if possible, rather than a NodeList.
* CSS selectors: You can use CSS selectors as part of your JavaScript code to select elements. This approach allows for more flexibility and power, but may also be slower due to the additional parsing step.

Keep in mind that these alternatives may require specific browser support or ECMAScript versions.

Related benchmarks:

querySelectorAll - vs - getElementsByClassName (version: 0)

Comparing performance of: getElementsByClassName vs querySelectorAll

Created: 7 years ago by: Guest

Jump to the latest result

getElementsByClassName

querySelectorAll

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

No previous run results

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