Benchmark: querySelectorAll() vs getElementsByTagName() - with constant length

HTML Preparation code:

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Tests:

querySelectorAll
document.querySelectorAll('a').forEach((element) => {});
getElementsByTagName
const tags = document.getElementsByTagName('a'); const l = tags.length; for (let i = 0; i < l; i++) {}

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
querySelectorAll
getElementsByTagName

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 dive into the benchmark and explain what's being tested.

**What is being tested?**

The benchmark compares the performance of two DOM querying methods:

1. `querySelectorAll()` (short for "query selector all")
2. `getElementsByTagName()`

Both methods are used to retrieve a collection of elements that match a specific CSS selector or tag name, respectively. However, they have different implementations and usage patterns.

**Options being compared:**

The benchmark compares the performance of each method with a constant length of 10 elements (in this case, `<a>` tags). The test is designed to measure which method is faster for small to medium-sized collections.

**Pros and Cons of each approach:**

1. `querySelectorAll()`:
	* Pros:
		+ Faster because it's a single operation that returns an array-like object.
		+ More flexible, as it can match multiple selectors using commas (e.g., `"a, img"`).
	* Cons:
		+ May have more overhead due to the need for parsing and compiling the CSS selector.
2. `getElementsByTagName()`:
	* Pros:
		+ Simpler to implement and parse, as it only needs to know the tag name.
	* Cons:
		+ Slower because it requires iterating over the length of the collection and processing each element individually.

**Library and purpose:**

There is no specific library being used in this benchmark. However, the `querySelectorAll()` method relies on the W3C standard for CSS selectors, which is a widely adopted and maintained specification.

**Special JavaScript feature or syntax:**

None mentioned in this benchmark.

**Other alternatives:**

For larger collections, other DOM querying methods may be faster:

1. `getElementsByClassName()`: Similar to `querySelectorAll()` but uses the class name instead of a CSS selector.
2. `getElementById()`: Retrieves an element by its ID attribute instead of using a CSS selector or tag name.

These alternatives may have different performance characteristics, depending on the specific use case and collection size.

**Benchmark preparation code:**

The script preparation code is empty, indicating that no additional setup or processing is needed for these benchmark cases. The HTML preparation code creates an HTML document with 10 `<div>` elements and 10 `<a>` tags, which will be used as the test subject.

Related benchmarks:

querySelectorAll() vs getElementsByTagName() - with constant length (version: 0)

Comparing performance of: querySelectorAll vs getElementsByTagName

Created: 2 years ago by: Guest

Jump to the latest result

querySelectorAll

getElementsByTagName

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):