Benchmark: querySelector versus getElementsByClassName

HTML Preparation code:

<div class="test"></div>

Tests:

querySelector
document.querySelector('.test').className;
getElementsByClassName
document.getElementsByClassName('test')[0].className;

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
querySelector
getElementsByClassName

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 3 years ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/88.0.4324.151 Safari/537.36

Browser/OS: Chrome 88 on Windows

View result in a separate tab

Test name	Executions per second
querySelector	2459318.5 Ops/sec
getElementsByClassName	2297260.5 Ops/sec

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

LLMs can make mistakes. Check important info.

**What is tested:**
MeasureThat.net tests the performance difference between two approaches to dynamically retrieve elements from an HTML document:

1. `document.querySelector('.test')` (using the `querySelector` method)
2. `document.getElementsByClassName('test')[0].className` (using the `getElementsByClassName` method)

These methods are used to select DOM elements based on their class names.

**Options compared:**
The benchmark compares two options:

1. **`querySelector`**: A modern, efficient way to select elements by CSS selector.
2. **`getElementsByClassName`**: An older method that returns an array of elements with the specified class name.

**Pros and Cons:**

* **`querySelector`**:
	+ Pros:
		- More efficient and faster (as shown in the benchmark results)
		- Can select multiple elements using a single query
		- Returns the first matching element, making it more convenient for simple use cases
	+ Cons:
		- May not work as expected if the DOM structure changes or is not optimized for `querySelector`
		- May have limitations when dealing with complex CSS selectors or large datasets
* **`getElementsByClassName`**:
	+ Pros:
		- Works consistently across different browsers and DOM structures
		- Can be used to select elements even if they don't match exactly (by using the `*=x` syntax)
	+ Cons:
		- Returns an array of all matching elements, which can be slower and more memory-intensive than `querySelector`
		- Less convenient for simple use cases, as it returns multiple elements

**Library usage:**
None of the test cases explicitly uses any JavaScript libraries. However, MeasureThat.net is likely using a library or framework to manage the benchmarking process.

**Special JS features/syntax:**
There are no special JavaScript features or syntax mentioned in this benchmark definition.

**Other alternatives:**
If you're interested in exploring alternative approaches for selecting elements from the DOM, here are a few options:

1. **`querySelectorAll`**: Similar to `querySelector`, but returns all matching elements instead of just one.
2. **`document.getElementsByTagName`**: Returns an array of all elements with the specified tag name.
3. **`DOMQuery` libraries**: There are several third-party libraries that provide more advanced and flexible DOM querying capabilities, such as jQuery or Sizzle.

Keep in mind that these alternatives may have their own performance characteristics and trade-offs, so it's essential to evaluate them based on your specific use case and requirements.

Related benchmarks:

querySelector versus getElementsByClassName (version: 0)

Comparing performance of: querySelector vs getElementsByClassName

Created: 3 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 llama3.2:3b, generated 2 months ago):