Benchmark: getElementById vs QuerySelector nested element

HTML Preparation code:


<div id="testElmt">
  <p>paragraph</p>
</div>

Tests:

getElementById + firstElementChild
const par = document.getElementById("testElmt").firstElementChild;
querySelector
const par = document.querySelector("#testElmt p");

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
getElementById + firstElementChild
querySelector

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 11 months ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/137.0.0.0 Safari/537.36

Browser/OS: Chrome 137 on Windows

View result in a separate tab

Test name	Executions per second
getElementById + firstElementChild	17646776.0 Ops/sec
querySelector	4422305.5 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's break down the provided benchmark and explain what's being tested.

**Benchmark Overview**

The benchmark measures the performance difference between using `document.getElementById` with `firstElementChild` vs using `document.querySelector` to select an element nested within another element.

**Options Compared**

There are two options being compared:

1. **`document.getElementById("testElmt").firstElementChild`**: This approach uses the `getElementById` method to get a reference to the element with the ID "testElmt", and then calls `firstElementChild` on that element to get a reference to its first child element.
2. **`document.querySelector("#testElmt p")`**: This approach uses the `querySelector` method to select an element with the ID "testElmt" and a tag name of "p".

**Pros and Cons**

1. **`document.getElementById("testElmt").firstElementChild`**:
	* Pros: More explicit and controlled way of selecting elements, can be more efficient if the DOM structure is known.
	* Cons: May lead to slower performance if the element or its child is not found, and may require additional lookup in case of multiple matching elements.
2. **`document.querySelector("#testElmt p")`**:
	* Pros: More concise and easier to read, can be faster for complex DOM structures where `querySelectorAll` can retrieve a list of all matches at once.
	* Cons: May lead to slower performance if the selector is ambiguous or returns multiple elements.

**Library/Language Features**

Neither option uses any specific library or language feature. However, it's worth noting that this benchmark assumes a standard JavaScript environment without any external libraries or modifications.

**Special JS Feature/Syntax**

There are no special JavaScript features or syntax used in these test cases. Both `getElementById` and `querySelector` are part of the DOM API and do not rely on any specific language features.

**Other Alternatives**

If you're interested in exploring alternative approaches, consider:

1. **`document.querySelectorAll`**: Similar to `querySelector`, but returns a NodeList of all matching elements.
2. **`getElementsByClassName`**: Returns an HTMLCollection of elements with the specified class name.
3. **CSS Selectors**: Modern browsers support CSS selectors like `:has`, `>`, and `~` for more complex element selection.

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

I hope this explanation helps! Let me know if you have any further questions.

Related benchmarks:

getElementById vs QuerySelector nested element (version: 0)

Comparing performance of: getElementById + firstElementChild vs querySelector

Created: 6 years ago by: Guest

Jump to the latest result

getElementById + firstElementChild

querySelector

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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