Benchmark: querySelector vs getElementsByClassName

HTML Preparation code:

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Tests:

querySelector
document.querySelector(".test")
getElementsByClassName
document.getElementsByClassName(".test")

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
querySelector
getElementsByClassName

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.1:latest, generated 27 days ago):

LLMs can make mistakes. Check important info.

Let's dive into the explanation.

**Benchmark Overview**

This benchmark tests two different methods for selecting HTML elements using JavaScript: `document.querySelector` and `document.getElementsByClassName`.

**What is being tested?**

Both test cases are trying to select an element with a specific class name (`".test"`) from the provided HTML code. The main difference between the two test cases lies in the method used to achieve this selection.

**Test Case 1: document.querySelector(".test")**

* **Method**: `document.querySelector`
* **Library/Library-Free**: Library-free, which means it doesn't rely on any external libraries or frameworks.
* **JavaScript Feature/Syntax**: Uses the modern `querySelector` method, which is part of the HTML5 specification.
* **Pros**:
	+ Fast and efficient, especially for selecting single elements.
	+ Supports CSS3 selectors (e.g., `.test`, `#id`, `[attribute]`, etc.).
* **Cons**:
	+ Returns a NodeList containing one element or an empty list if no matching elements are found.
* **Considerations**: When using `querySelector`, it's essential to ensure the CSS selector is correct and efficient, as incorrect or complex selectors can lead to slower performance.

**Test Case 2: document.getElementsByClassName(".test")**

* **Method**: `document.getElementsByClassName`
* **Library/Library-Free**: Library-free, just like the previous test case.
* **JavaScript Feature/Syntax**: Uses the older `getElementsByClassName` method, which returns a HTMLCollection of all elements with the specified class name.
* **Pros**:
	+ Supports multiple selections and returns an array-like collection.
	+ May be more suitable when working with dynamic or complex DOM structures.
* **Cons**:
	+ Returns a live collection, meaning it's updated as the DOM changes.
	+ Can lead to slower performance due to the overhead of maintaining a live collection.

**Other Considerations**

When choosing between `querySelector` and `getElementsByClassName`, consider the following:

1. **Single element selection**: If you're selecting a single element, use `querySelector`. It's faster and more efficient.
2. **Multiple element selection**: If you need to select multiple elements with the same class name, use `getElementsByClassName`.
3. **Dynamic DOM**: In dynamic environments where the DOM is frequently updated, consider using `getElementsByClassName` to ensure your selections remain accurate.
4. **CSS selectors**: When working with CSS3 selectors (e.g., `.test`, `#id`, `[attribute]`, etc.), use `querySelector`.

**Alternatives**

If you're looking for alternative methods or libraries, consider the following:

1. **Lodash's `$` function**: Lodash provides a convenience function called `$` that can be used to select elements using CSS selectors.
2. **jQuery**: jQuery is a popular JavaScript library with its own method, `$(selector)`, for selecting elements.
3. **QuerySelectorAll**: This method returns all elements matching the specified CSS selector as a NodeList.

Remember, when choosing between these alternatives, consider the specific requirements of your project and the performance implications of each approach.

Latest run results:

Run details: (Test run date: 6 years ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/66.0.3359.139 Safari/537.36

Browser/OS: Chrome 66 on Windows

View result in a separate tab

Test name	Executions per second
querySelector	249093.2 Ops/sec
getElementsByClassName	1983676.2 Ops/sec

Related benchmarks:

querySelector vs getElementsByClassName (version: 0)

Comparing performance of: querySelector vs getElementsByClassName

Created: 6 years ago by: Guest

Jump to the latest result

querySelector

getElementsByClassName

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.1:latest, generated 27 days ago):