Benchmark: querySelector vs getElementsByClassName

HTML Preparation code:

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

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 llama3.2:3b, generated one month ago):

LLMs can make mistakes. Check important info.

I'd be happy to help you understand the JavaScript microbenchmark on MeasureThat.net.

**What is being tested?**

The benchmark compares two methods for selecting HTML elements from a document: `document.querySelector()` and `document.getElementsByClassName()`. These two methods are used to retrieve DOM elements that match a specific CSS selector or class name, respectively.

**Options compared:**

There are only two options compared:

1. **`document.querySelector()`**: This method is used to select the first element that matches the specified CSS selector. It returns a single element if found, and `null` otherwise.
2. **`document.getElementsByClassName()`**: This method returns an HTMLCollection (a live collection of elements) that contains all elements with the specified class name.

**Pros and Cons:**

1.  **`document.querySelector()`**
    *   Pros:
        *   More versatile and powerful than `getElementsByClassName()`, as it can select elements based on any CSS selector, not just classes.
        *   Returns a single element if found, which can be more efficient for selecting a specific element.
    *   Cons:
        *   May return `null` if no matching element is found, requiring additional checks to ensure the result is valid.
2.  **`document.getElementsByClassName()`**
    *   Pros:
        *   Returns all elements with the specified class name, which can be useful for finding multiple elements at once.
        *   Does not require checking for `null` values like `querySelector()` does.
    *   Cons:
        *   Less powerful and flexible than `querySelector()`, as it only supports class names and no other CSS selectors.

**Library:**

The benchmark uses the following JavaScript library:

*   **None**: This benchmark does not use any external libraries, as it is a basic comparison of built-in DOM methods.

**Special JS feature or syntax:**

There are no special JavaScript features or syntax mentioned in this benchmark. However, if you're interested in learning about some advanced topics, the benchmark might touch on concepts like:

*   **CSS selectors**: Used by `document.querySelector()` to select elements based on various criteria.
*   **HTMLCollection**: The data structure returned by `getElementsByClassName()`, which is a live collection of elements.

**Other alternatives:**

If you're looking for alternative methods to compare, consider the following:

*   **`document.querySelectorAll()`**: A method similar to `querySelector()`, but returns a NodeList (a live HTML collection) instead of a single element.
*   **`Array.prototype.filter()` or other array methods**: Can be used to filter elements based on certain conditions, providing an alternative to DOM selection methods.

In conclusion, this benchmark helps you understand the performance differences between two widely used DOM methods in JavaScript: `document.querySelector()` and `document.getElementsByClassName()`. The results can help you decide when to use each method based on your specific needs.

Latest run results:

Run details: (Test run date: 5 years ago)

User agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/70.0.3538.110 Safari/537.36

Browser/OS: Chrome 70 on Windows 7

View result in a separate tab

Test name	Executions per second
querySelector	2160853.0 Ops/sec
getElementsByClassName	2568132.8 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 llama3.2:3b, generated one month ago):