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

Latest run results:

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

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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.

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: 7 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>

Fastest: N/A

Slowest: N/A

No previous run results

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