Benchmark: querySelector vs querySelector 4

HTML Preparation code:

<div id="foo"></div>
<div class="bar"></div>
<div class="zaz"></div>
<div class="tal"></div>
<div class="quq"></div>
<div class="foo"></div>

Tests:

class
document.querySelector('.foo')
id
document.querySelector('#foo')

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
class
id

Fastest: N/A

Slowest: N/A

Latest run results:

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Autogenerated LLM Summary (model llama3.1:latest, generated one year ago):

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Let's break down what's being tested here.

**Benchmark Definition**

The benchmark tests two different ways of selecting an HTML element using the `querySelector` method in JavaScript:

1. **Selector by Class**: `document.querySelector('.foo')`
2. **Selector by ID**: `document.querySelector('#foo')`

These are two alternative approaches to achieve the same result: selecting a specific HTML element on the page.

**What's being compared**

In this benchmark, we're comparing the performance of two different selectors:

* `.foo`: Selects an HTML element with the class "foo".
* `#foo`: Selects an HTML element with the ID "foo".

The test cases use the same HTML preparation code, which contains several elements with different IDs and classes.

**Pros/Cons of each approach**

* **Selector by Class**: This approach is faster because it's more specific. When the browser encounters a CSS class selector, it can often skip unnecessary DOM traversal.
	+ Pros: Faster execution time
	+ Cons: May not work if multiple elements have the same class (although this is unlikely in this test case)
* **Selector by ID**: This approach is slower because it's more specific and requires the browser to search for an element with a unique ID.
	+ Pros: Guaranteed uniqueness of selection (no possibility of selecting wrong element)
	+ Cons: Slower execution time

**Other considerations**

When using `querySelector` or `querySelectorAll`, keep in mind:

* **Performance**: If you have multiple elements with the same class, using a CSS class selector might be faster.
* **Uniqueness**: When using an ID selector, make sure the element has a unique ID to avoid unexpected behavior.

**Library and purpose**

No external library is used in this benchmark. The `querySelector` method is part of the standard JavaScript API for working with HTML documents.

**Special JS feature or syntax**

None are used in this test case.

**Other alternatives**

If you need to select an element by a different attribute (e.g., data-attribute), you could use:

* `document.querySelector('[data-foo="bar"]')`
* `document.querySelector('[foo-bar]')` (not recommended, as it's more prone to errors)

Keep in mind that these alternatives might have different performance characteristics depending on the specific use case and browser implementation.

Related benchmarks:

querySelector vs querySelector 4 (version: 0)

Comparing performance of: class vs id

Created: 6 years ago by: Guest

Jump to the latest result

class

id

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

No previous run results

Autogenerated LLM Summary (model llama3.1:latest, generated one year ago):