Benchmark: parent vs document queryselectorAll

HTML Preparation code:

<div id="main">
<div><div><div><div><div><div>
  
<div id="parent">
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
</div>

</div></div></div></div></div></div>
</div>

Script Preparation code:

var main = document.querySelector('#main');
var parent = document.querySelector('#parent');

Tests:

parent.querySelector
var child = parent.querySelectorAll('.child');
document.querySelector
var child = main.querySelectorAll('#parent .child');
document.querySelector 2
var child = main.querySelectorAll('.child');

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
parent.querySelector
document.querySelector
document.querySelector 2

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 24 days ago):

LLMs can make mistakes. Check important info.

Let's dive into the explanation of the benchmark.

**Benchmark Definition JSON**

The benchmark is designed to measure the performance difference between using `parent.querySelector` and `document.querySelector`. The script preparation code sets up two variables, `main` and `parent`, by querying the HTML document for elements with IDs `#main` and `#parent`, respectively. The HTML preparation code creates a nested structure of divs with class `child`.

**Individual Test Cases**

There are three test cases:

1. `parent.querySelector`: This test case uses the `parent.querySelector` method to query all elements with class `child`. It first queries for the parent element (`#parent`) and then uses `querySelectorAll` on that element.
2. `document.querySelector 2`: This test case uses a slightly different syntax, using two separate queries: one for the main element (`#main`) and another for an element inside it with class `child`. The number in the test name suggests that this is a variant of the previous test case.
3. `document.querySelector`: This is the same as test case 2, but without the additional query.

**Library Used**

In all test cases, the `querySelectorAll` method is used to query elements with class `child`. The `querySelector` method is used in conjunction with these calls. These methods are part of the DOM (Document Object Model) API and provide a way to select elements based on their tag name, id, class, attribute, or CSS selector.

**Special JS Feature/Syntax**

There doesn't seem to be any special JavaScript features or syntax used in these test cases. The syntax is straightforward and follows standard ECMAScript rules.

**Pros and Cons of Different Approaches**

1. `parent.querySelector`:
	* Pros: May be faster due to the caching effect, as it only queries for the parent element once.
	* Cons: Requires a separate query for the child elements, which may add overhead.
2. `document.querySelector 2` (and `document.querySelector`):
	* Pros: Avoids the need for an additional query, making it potentially faster than `parent.querySelector`.
	* Cons: Requires two separate queries, which may increase overall overhead.

**Other Considerations**

1. **Caching**: The `querySelectorAll` method uses caching to improve performance. However, this effect is only noticeable if the same selector is used multiple times in a short amount of time.
2. **DOM Traversal**: The `querySelectorAll` method traverses the DOM tree starting from the given element (in this case, `parent` or `main`). This can lead to slower performance if the element has many descendants.

**Alternatives**

If you're interested in exploring alternative approaches:

1. **Use `document.querySelectorAll` with a CSS selector**: Instead of using `querySelectorAll`, try using the CSS selector syntax (e.g., `.child`) to query elements.
2. **Try `Array.prototype.slice.call(document.querySelectorAll('.child'))`**: This approach uses `slice.call` to convert the NodeList returned by `document.querySelectorAll` into an array, which can be used with other array methods.
3. **Experiment with different DOM traversal techniques**: Depending on your specific use case, you might find that using a more targeted DOM traversal technique (e.g., `Element.children`) or even using libraries like jQuery can provide better performance.

Keep in mind that these alternatives may introduce additional complexity and may not always lead to better performance.

Latest run results:

Run details: (Test run date: 2 years ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/106.0.0.0 Safari/537.36

Browser/OS: Chrome 106 on Windows

View result in a separate tab

Test name	Executions per second
parent.querySelector	984672.4 Ops/sec
document.querySelector	468034.7 Ops/sec
document.querySelector 2	904307.8 Ops/sec

Related benchmarks:

parent vs document queryselectorAll (version: 1)

Comparing performance of: parent.querySelector vs document.querySelector vs document.querySelector 2

Created: 7 years ago by: Registered User

Jump to the latest result

parent.querySelector

document.querySelector

document.querySelector 2

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 24 days ago):