Benchmark: querySelectorAll vs. getElementsByClassName

HTML Preparation code:

<div class="test">0</div>

Tests:

querySelectorAll
document.querySelectorAll(".test").forEach( test => console.log(test.innerHTML))
getElementsByClassName
Array.prototype.forEach.call(document.getElementsByClassName("test"), function(test) { console.log(test.innerHTML) });

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:

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

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

**Benchmark Definition**

The benchmark is comparing two approaches to select elements from an HTML document:

1. `querySelectorAll`: This method returns a NodeList containing all child elements that match the specified CSS selector, in this case, `.test`.
2. `getElementsByClassName`: This method returns a DOMCollection (an array-like object) of all elements that have the specified class name, also `.test`.

**Options Compared**

The two options being compared are:

* `querySelectorAll`: Returns a NodeList, which is live and updates when the document changes.
* `getElementsByClassName`: Returns a DOMCollection, which is static and doesn't update when the document changes.

**Pros and Cons**

**`querySelectorAll`**

Pros:

* Live results: The NodeList is updated in real-time as the document changes.
* Easy to use: Simple syntax and intuitive API.

Cons:

* Performance overhead: Since `querySelectorAll` returns a live NodeList, it may incur additional processing costs compared to static DOMCollection.

**`getElementsByClassName`**

Pros:

* Performance benefits: Since `getElementsByClassName` returns a static DOMCollection, it may be faster than `querySelectorAll`.

Cons:

* Less intuitive API: The `getElementsByClassName` method is less straightforward than `querySelectorAll`.
* Potential for stale results: If the document changes between executions, the DOMCollection might not reflect the updated content.

**Library Usage**

There is no explicit library usage mentioned in this benchmark. However, it's worth noting that both methods rely on the Document Object Model (DOM) and CSS selectors.

**Special JS Feature or Syntax**

Neither of these options utilizes special JavaScript features or syntax beyond standard DOM and CSS selector APIs.

**Other Alternatives**

If you're interested in exploring alternative approaches:

* `querySelector` (similar to `querySelectorAll`, but returns a single element instead of a NodeList).
* `getElementsByTagName` (returns a DOMCollection of elements with the specified tag name, without the need for classes or IDs).
* Modern alternatives like `querySelectorAll( )` with the `useCapture` property can be used to specify whether the results should be live or not.

**Benchmark Preparation Code**

The provided HTML preparation code creates a simple `<div>` element with the class `test`, which is used as the target for both selectors:

```html
"<div class=\"test\">0</div>"
```

This benchmark can help measure the performance difference between these two commonly used methods in JavaScript, particularly when working with dynamic content or large datasets.

Related benchmarks:

querySelectorAll vs. getElementsByClassName (version: 0)

Comparing performance of: querySelectorAll vs getElementsByClassName

Created: 2 years ago by: Guest

Jump to the latest result

querySelectorAll

getElementsByClassName

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):