Benchmark: querySelector vs getElementsByClassName

HTML Preparation code:

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

Tests:

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

Historical Performance Data aggregated from 56 community runs

Desktop Results:

Chrome 41 runs

getElementsByClassName

8.5M/s

querySelector

6.9M/s

Fastest: getElementsByClassName (1.2x faster)

View exact numbers

✓ getElementsByClassName: 8,490,356 ops/sec
• querySelector: 6,945,901 ops/sec

Firefox 15 runs

getElementsByClassName

8.1M/s

querySelector

4.5M/s

Fastest: getElementsByClassName (1.8x faster)

View exact numbers

✓ getElementsByClassName: 8,125,064 ops/sec
• querySelector: 4,547,580 ops/sec

Results show median performance across all community submissions. Run this benchmark yourself to verify on your device.

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: 10 months ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:145.0) Gecko/20100101 Firefox/145.0

Browser/OS: Firefox 145 on Mac OS X 10.15

View result in a separate tab

getElementsByClassName

7.1M/s

querySelector

4.3M/s

View exact numbers

Test name	Executions per second
✓ getElementsByClassName	7,097,863 Ops/sec
querySelector	4,276,726 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 benchmark and its options.

**Benchmark Overview**

The provided benchmark compares two methods for selecting elements in an HTML document using JavaScript: `document.querySelector()` (querySelector) and `document.getElementsByClassName()` (getElementsByClassName). The goal is to determine which method performs better in terms of execution speed.

**Options Compared**

1. **querySelector**: This method uses a CSS selector to select the first element that matches a specified pattern. In this case, it's used with the class "test".
2. **getElementsByClassName**: This method returns a live HTMLCollection of all elements whose class attribute contains the specified value ("test" in this case).

**Pros and Cons**

1. **querySelector**:
	* Pros:
		+ Faster execution time due to its optimized CSS selector implementation.
		+ More flexible and powerful for complex selectors.
		+ Returns a single element, making it easier to work with individual elements.
	* Cons:
		+ May not be supported in older browsers (before IE9).
		+ Requires the element to have a class attribute.
2. **getElementsByClassName**:
	* Pros:
		+ Supported by most modern browsers, including older versions of Internet Explorer.
		+ Does not require an explicit class attribute on the element.
	* Cons:
		+ Returns an HTMLCollection, which can be slower and less efficient than working with individual elements.
		+ Requires specifying the exact class name.

**Library Usage**

None of the provided methods rely on any external libraries. They are built-in JavaScript methods for interacting with the DOM.

**Special JavaScript Features or Syntax**

Neither method utilizes special JavaScript features or syntax beyond basic JavaScript programming.

**Alternative Approaches**

Other alternatives to consider:

1. **document.querySelectorAll()**: Similar to `querySelector`, but returns a NodeList of all elements that match the specified pattern.
2. **CSSOM methods**: The CSS Object Model (CSSOM) provides other methods for selecting elements, such as `document.querySelectorAll()` and `window.matchMedia()`. These methods can offer more flexibility and power than the basic DOM methods used in this benchmark.

Keep in mind that these alternatives may introduce additional overhead or complexity, so it's essential to evaluate their performance characteristics before using them in production code.

querySelector vs getElementsByClassName (version: 0) Benchmark.js

Comparing performance of: `querySelector vs getElementsByClassName`

Created: 9 years ago by: Registered User

Go to the latest result

querySelector

getElementsByClassName

Historical Performance Data aggregated from 56 community runs

Desktop Results:

Chrome 41 runs

Firefox 15 runs

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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

querySelector vs getElementsByClassName (version: 0) Benchmark.js

Comparing performance of: querySelector vs getElementsByClassName

Created: 9 years ago by: Registered User

Go to the latest result

querySelector

getElementsByClassName

Historical Performance Data aggregated from 56 community runs

Desktop Results:

Chrome 41 runs

Firefox 15 runs

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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

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Comparing performance of: `querySelector vs getElementsByClassName`