Benchmark: QuerySelector vs Get First Element By Tag Name

HTML Preparation code:

<a class="test"></a>
<b class="test2"></b>
<i class="test3"></i>
<p class="test4"></p>

Tests:

querySelector Tag
document.querySelector("A")
getElementsByTagName(TAG)[0]
document.getElementsByTagName("A")[0]

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
querySelector Tag
getElementsByTagName(TAG)[0]

Fastest: N/A

Slowest: N/A

Latest run results:

No previous run results

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

LLMs can make mistakes. Check important info.

I'd be happy to explain the JavaScript microbenchmark on MeasureThat.net.

**What is being tested?**

The benchmark is testing two ways to select an element by its tag name:

1. `querySelector`: This method returns the first element that matches the specified selector, or null if no elements match.
2. `getElementsByTagName` followed by `[0]`: This method returns a list of all elements with the specified tag name, and then returns the first element in that list (index 0).

**Options compared**

The benchmark is comparing these two approaches to select an element by its tag name:

* `querySelector`
* `getElementsByTagName(TAG)[0]`

Both methods have their own strengths and weaknesses.

**Pros and Cons:**

1. **`querySelector`**
	* Pros:
		+ More concise and readable code
		+ Only matches the first occurrence of the specified selector, which can be faster for large datasets
	* Cons:
		+ May not work correctly if the selector is complex or uses pseudo-elements
		+ Can be slower than `getElementsByTagName` in some cases (see below)
2. **`getElementsByTagName(TAG)[0]`**
	* Pros:
		+ Works with all elements, regardless of their type or class
		+ Allows for more precise control over the selection process
	* Cons:
		+ More verbose code
		+ May be slower than `querySelector` in some cases (see below)

**Performance comparison**

The performance difference between these two approaches depends on various factors, such as:

* The number of elements with the specified tag name
* The complexity of the selector or method used to select the element
* The specific browser and version being tested

In general, `querySelector` is faster than `getElementsByTagName(TAG)[0]` when:

* Only one element needs to be selected
* The selector is simple and doesn't use pseudo-elements

On the other hand, `getElementsByTagName(TAG)[0]` may be faster when:

* Multiple elements need to be selected (although `querySelector` can also handle this with a comma-separated list)
* Complex selectors are used (although these can slow down both methods)

**Library usage**

There is no library being tested in this benchmark.

**Special JS features or syntax**

This benchmark doesn't use any special JavaScript features or syntax, so it should be understandable to most software engineers without deep knowledge of JavaScript.

**Other alternatives**

If you need to select elements by tag name and performance is a concern, you may also consider using:

* `querySelectorAll(TAG)` followed by `[0]`, which returns all elements with the specified tag name and then returns the first element in the resulting NodeList
* Regular expressions (regex) to match elements by tag name

However, these alternatives are generally less efficient than `querySelector` or `getElementsByTagName(TAG)[0]`.

Related benchmarks:

QuerySelector vs Get First Element By Tag Name (version: 1)

test querySelector vs getElementsByTagName when only one of that tag exists

Comparing performance of: querySelector Tag vs getElementsByTagName(TAG)[0]

Created: 5 years ago by: Registered User

Jump to the latest result

querySelector Tag

getElementsByTagName(TAG)[0]

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):