Benchmark: document getElementsByTagName vs querySelectorAll

HTML Preparation code:

<div></div>
<div></div>
<div></div>
<div></div>
<div></div>
<div></div>
<div></div>
<div></div>
<div></div>
<div></div>

Tests:

getElementsByTagName
document.getElementsByTagName('div')
querySelectorAll
document.querySelectorAll('div')

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
getElementsByTagName
querySelectorAll

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 12 days ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/135.0.0.0 Safari/537.36 Edg/135.0.0.0

Browser/OS: Chrome 135 on Windows

View result in a separate tab

Test name	Executions per second
getElementsByTagName	28991550.0 Ops/sec
querySelectorAll	3457444.8 Ops/sec

Autogenerated LLM Summary (model gpt-4o-mini, generated 12 days ago):

LLMs can make mistakes. Check important info.

The benchmark you provided compares two methods for retrieving elements from the DOM (Document Object Model) in a web page using JavaScript: `document.getElementsByTagName` and `document.querySelectorAll`. Below, I elaborate on each method, their performance outcomes, and considerations for software engineers.

### Methods Being Compared

1. **`document.getElementsByTagName('div')`**
   - **Functionality**: This method retrieves all elements in the document with a specified tag name (in this case, 'div'). It returns a live HTMLCollection of elements, which means that if the DOM changes (elements are added or removed), the collection updates automatically.
   - **Pros**:
     - Efficient for direct tag searches since it directly queries the tag name.
     - Live collection can be beneficial if the resulting set is used with changing elements.
   - **Cons**:
     - The returned HTMLCollection is not an array, which may require additional conversion for array-like operations.
     - The live nature of the collection can lead to unexpected behavior if the DOM is modified while iterating over the collection.

2. **`document.querySelectorAll('div')`**
   - **Functionality**: This method returns a static NodeList of all elements matching a specified CSS selector (here, all 'div' elements). Unlike `getElementsByTagName`, it uses CSS selector syntax.
   - **Pros**:
     - The method is more versatile, as it allows for more complex selectors beyond just tag names (e.g., classes, IDs, attributes).
     - The returned NodeList is static, meaning it does not change when the DOM is modified, which can make handling results more predictable and simpler.
   - **Cons**:
     - Generally slower than `getElementsByTagName` for simple tag searches since it has to parse the selector.
     - Doesn’t provide live updates if the DOM changes, which might not be suitable for scenarios needing dynamic updates.

### Performance Results

The benchmark results show the number of times each method executed per second:

- **`getElementsByTagName`**: 28,991,550 executions per second.
- **`querySelectorAll`**: 3,457,444.75 executions per second.

From these results, it’s clear that `getElementsByTagName` significantly outperforms `querySelectorAll` in this specific test case. When retrieving simple tag elements, `getElementsByTagName` is almost eight times faster than `querySelectorAll`.

### Other Considerations

- **Use Cases**: Choosing between these two methods should be based on the specific use case. If you only need to select elements by their tag and expect frequent DOM changes, `getElementsByTagName` may be suitable. If you require more complex selections or prefer static lists to avoid unintended consequences from live collections, `querySelectorAll` would be preferable.
  
- **Browser Compatibility**: Both methods are widely supported across modern browsers, but performance can vary based on the browser engine and version. The benchmark was conducted on Chrome 135, showing specific performance metrics that might differ in other browsers or versions.

- **Alternatives**: In addition to these two methods, there are also various libraries such as jQuery that abstract DOM manipulation and querying, although they may introduce additional overhead in terms of file size and performance in some scenarios. Modern frameworks like React or Vue.js provide their own mechanisms to interact with the DOM that might be preferred depending on the context of the application.

In summary, the benchmark demonstrates a clear performance advantage for `getElementsByTagName` in this scenario, but the choice should always be guided by the specific requirements and characteristics of the project being developed.

Related benchmarks:

document getElementsByTagName vs querySelectorAll (version: 1)

Comparing performance of: getElementsByTagName vs querySelectorAll

Created: 12 days ago by: Guest

Jump to the latest result

getElementsByTagName

querySelectorAll

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model gpt-4o-mini, generated 12 days ago):