Benchmark: compare querySelector nested vs getElementById

HTML Preparation code:

<div id="id-up">
  <div id="nested">
    <div id="nested-2" class="nestme"></div>
  </div>
 </div>

Tests:

get to nested 2 by getElementById
var el1 = document.getElementById("id-up"); var el2 = document.getElementById("nested-2"); var className = el2.className;
get to nested 2 by query selector
var el1 = document.getElementById("id-up"); var el2 = el1.querySelector("#nested-2"); var className = el2.className;

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
get to nested 2 by getElementById
get to nested 2 by query selector

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 27 days ago):

LLMs can make mistakes. Check important info.

Let's dive into the benchmarking process.

The provided JSON represents two test cases that compare the performance of two approaches: using `document.getElementById` (also known as inline DOM access) versus using the query selector API (`querySelector`).

**What is tested?**

In each test case, we're trying to retrieve an element by its ID and then extract a CSS class from that element.

**Options compared**

We have two options:

1. **Inline DOM access**: `document.getElementById("id-up");`, `var el2 = document.getElementById("nested-2");`
	* Pros:
		+ Simple, straightforward approach.
		+ No need to worry about the existence of an element with a specific ID.
	* Cons:
		+ Can be slower due to the following reasons:
			- DOM search is necessary to find the element by its ID.
			- The browser has to perform a full parse and rebuild of the DOM tree, which can lead to performance overhead.
2. **Query selector API**: `var el1 = document.getElementById("id-up");`, `var el2 = el1.querySelector("#nested-2");`
	* Pros:
		+ More efficient than inline DOM access because it leverages a pre-existing data structure (the CSS styles) that is faster to query.
		+ Allows for more flexibility and specificity in element selection.
	* Cons:
		+ Requires an existing element with the specified ID to exist in the DOM.

**Library**

The query selector API (`querySelector`) relies on CSS selectors, which are a part of the W3C standard. The library is built into modern browsers' JavaScript engines and doesn't require any external libraries.

**Special JS feature/syntax**

There's no special JavaScript feature or syntax involved here. These approaches are fundamental to DOM manipulation in JavaScript.

**Benchmark preparation code**

The provided HTML preparation code creates a simple DOM structure with nested elements:

```html
<div id="id-up">
  <div id="nested">
    <div id="nested-2" class="nestme"></div>
  </div>
</div>
```

This allows us to test the performance of retrieving elements by their IDs.

**Alternative approaches**

If we wanted to explore other alternatives, we might consider:

1. Using `document.querySelector` with a CSS selector that targets the element directly (e.g., `#nested-2.nestme`). This would bypass the need for inline DOM access.
2. Using a library like jQuery, which provides its own method for accessing elements by their IDs (e.g., `$("#id-up").find("#nested-2").className;`).
3. Using a more recent feature like `element.closest()` or `element.parents()` to traverse the DOM and retrieve elements.

However, these alternatives might introduce additional dependencies, complexity, or overhead, so they may not be worth exploring in this specific benchmarking scenario.

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
get to nested 2 by getElementById	2281845.5 Ops/sec
get to nested 2 by query selector	2993521.0 Ops/sec

Related benchmarks:

compare querySelector nested vs getElementById (version: 0)

Comparing performance of: get to nested 2 by getElementById vs get to nested 2 by query selector

Created: 6 years ago by: Guest

Jump to the latest result

get to nested 2 by getElementById

get to nested 2 by query selector

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 27 days ago):