Benchmark: querySelector scope vs no scope

HTML Preparation code:

<div id='parent'>
  <div class="foo">
    <div class="bar">
      <div class="baz">
      </div>
    </div>
  </div>
</div>

Script Preparation code:

let parent = document.getElementById('parent');

Tests:

querySelector scope
document.getElementById("parent").querySelector(':scope .baz')
querySelector no scope
document.getElementById("parent").querySelector('.baz')

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
querySelector scope
querySelector no scope

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: one year ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:130.0) Gecko/20100101 Firefox/130.0

Browser/OS: Firefox 130 on Windows

View result in a separate tab

querySelector no scope

3.5M/s

querySelector scope

2.8M/s

View exact numbers

Test name	Executions per second
✓ querySelector no scope	3,544,391 Ops/sec
querySelector scope	2,824,978 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's dive into the world of JavaScript microbenchmarks on MeasureThat.net!

**Benchmark Definition**

The provided JSON represents a benchmark definition for two test cases: `querySelector scope` and `querySelector no scope`. The goal is to compare the performance of using the `:scope` pseudo-class with and without it in the `querySelector` method.

**Options compared**

Two options are being compared:

1. **`:scope`**: Using the `:scope` pseudo-class in the `querySelector` method. This allows the query selector to only consider elements within the same scope (i.e., the parent element).
2. **No `:scope`**: Without using the `:scope` pseudo-class, the query selector will search for the specified class or ID across all ancestors of the current element.

**Pros and Cons**

**Using `:scope`:**

Pros:

* More efficient, as it reduces the number of elements to consider in the search.
* Can be beneficial when working with complex DOM structures.

Cons:

* May not work correctly if the pseudo-class is used on an ancestor element that's not a direct child.
* Might lead to unexpected results if the `:scope` pseudo-class is used incorrectly.

**Not using `:scope`:**

Pros:

* More flexible, as it allows for searching across all ancestors of the current element.
* Can be useful when working with elements that are not direct children of the query selector's context.

Cons:

* May be slower, especially in complex DOM structures, as more elements need to be considered.
* Can lead to performance issues if not used carefully.

**Library and purpose**

None of the provided benchmark definition JSON uses a JavaScript library. However, it does use HTML and CSS selectors.

If you're familiar with HTML and CSS selectors, you might have noticed that `:scope` is not a standard pseudo-class in CSS. It's actually a proprietary feature introduced by Mozilla (Firefox) to improve performance when working with `querySelector` methods. While not widely adopted, `:scope` has been used in various benchmarking tests, like this one.

**Special JS feature or syntax**

The test case uses the `:scope` pseudo-class, which is a proprietary feature of Mozilla's JavaScript engine (Gecko). It allows for efficient querying within a specific scope. This feature is not part of standard JavaScript and is mainly used to improve performance in certain scenarios.

Other alternatives

If you're interested in exploring alternative benchmarks or libraries, here are some options:

* **Benchmarking frameworks**: MeasureThat.net itself uses a custom benchmarking framework, but other popular ones include `jsperf`, ` Benchmark.js`, and `fastest`.
* **JavaScript engines**: You can explore benchmarking tests for different JavaScript engines, such as V8 (Google Chrome), SpiderMonkey (Firefox), or SquirrelFish (Safari).
* **Web performance benchmarks**: Websites like WebPageTest, Lighthouse, or PerformanceNow offer comprehensive web performance benchmarks and analysis tools.

In summary, this benchmark definition compares the performance of using `:scope` with and without it in the `querySelector` method. While not widely adopted, `:scope` has been used in various testing scenarios to improve performance when working with complex DOM structures.

querySelector scope vs no scope (version: 0) Benchmark.js

Comparing performance of: `querySelector scope vs querySelector no scope`

Created: 2 years ago by: Guest

Go to the latest result

querySelector scope

querySelector no scope

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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

querySelector scope vs no scope (version: 0) Benchmark.js

Comparing performance of: querySelector scope vs querySelector no scope

Created: 2 years ago by: Guest

Go to the latest result

querySelector scope

querySelector no scope

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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

Related benchmarks

Comparing performance of: `querySelector scope vs querySelector no scope`