Benchmark: querySelector vs getElementsByClassName with destructuring assignment

HTML Preparation code:

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

Tests:

querySelector
/*When writing async/deferred tests, use `deferred.resolve()` to mark test as done*/ const testElement = document.querySelector(".test");
getElementsByClassName with destructuring assignment
const [testElement] = document.getElementsByClassName(".test");

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
querySelector
getElementsByClassName with destructuring assignment

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: one year ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/133.0.0.0 Safari/537.36

Browser/OS: Chrome 133 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
querySelector	28673496.0 Ops/sec
getElementsByClassName with destructuring assignment	15922849.0 Ops/sec

Autogenerated LLM Summary (model gpt-4o-mini, generated one year ago):

LLMs can make mistakes. Check important info.

The provided benchmark compares two methods of selecting DOM elements in JavaScript: `document.querySelector` and `document.getElementsByClassName`, the latter using destructuring assignment.

### Options Compared

1. **`document.querySelector`**:
   - This method retrieves the first element within the document that matches a specified CSS selector. The syntax used in the benchmark is:
     ```javascript
     const testElement = document.querySelector(".test");
     ```

2. **`document.getElementsByClassName` using destructuring assignment**:
   - This method returns a live HTMLCollection of elements with the specified class name. By using destructuring, the benchmark retrieves the first element directly from the collection. The syntax is:
     ```javascript
     const [testElement] = document.getElementsByClassName(".test");
     ```

### Pros and Cons

#### `document.querySelector`
**Pros**:
- Supports any valid CSS selector, allowing for more complex and flexible selections (e.g., combining classes, IDs, or using pseudo-classes).
- Returns a single element, making it straightforward when only one match is needed.

**Cons**:
- Generally slower than `getElementsByClassName` for multiple elements since it involves parsing the CSS selector and can involve more overhead.

#### `document.getElementsByClassName`
**Pros**:
- Faster for selecting elements by class name, particularly when dealing with many elements in the DOM. This is because it directly accesses the class name rather than parsing a full CSS selector.
- Returns a live HTMLCollection, meaning any changes to the DOM will automatically reflect in the collection.

**Cons**:
- The syntax can be less intuitive, especially with destructuring if the intent is to access just one element.
- Limited to selection by class name only, lacking the flexibility of CSS selectors.

### Other Considerations
- **Performance**: The benchmark indicates that `querySelector` is significantly faster in this specific instance, with approximately 28.7 million executions per second compared to around 15.9 million for `getElementsByClassName` with destructuring.
- **Browser Compatibility**: Both methods are well-supported across all modern browsers, but performance may vary between different versions and implementations, as evident from the benchmark results.

### Alternative Approaches
- **`document.getElementById`**: If you're specifically looking for an element by ID, this method is the fastest as IDs are unique in a document.
- **`document.querySelectorAll`**: Similar to `querySelector`, but returns a NodeList of all matching elements, useful for case handling multiple elements.
- **Native DOM methods**: Increasingly, JavaScript libraries like React or Vue may abstract these selections into their frameworks, relying on virtual DOMs or similar techniques.

Overall, the choice between these methods depends on your specific use case, particularly considerations of performance versus flexibility in selector usage.

Related benchmarks:

querySelector vs getElementsByClassName with destructuring assignment (version: 1)

Comparing performance of: querySelector vs getElementsByClassName with destructuring assignment

Created: one year ago by: Guest

Jump to the latest result

querySelector

getElementsByClassName with destructuring assignment

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model gpt-4o-mini, generated one year ago):