Benchmark: document.body.getElementsByClassName vs document.getElementsByClassName +

HTML Preparation code:

<!DOCTYPE html>
<html lang="ru">
<head>
</head>
<body>
  <div class="aap">AAP</div>
</body>
</html>

Tests:

getElementsByClassName
const classElm = document.getElementsByClassName('aap')[0];
body.getElementsByClassName
const classElm = document.body.getElementsByClassName('aap')[0];

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
getElementsByClassName
body.getElementsByClassName

Fastest: N/A

Slowest: N/A

Latest run results:

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

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/109.0.0.0 Safari/537.36

Browser/OS: Chrome 109 on Windows

View result in a separate tab

Test name	Executions per second
getElementsByClassName	8804723.0 Ops/sec
body.getElementsByClassName	7221052.0 Ops/sec

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

LLMs can make mistakes. Check important info.

The benchmark described in the provided JSON compares two methods for selecting DOM elements in JavaScript, specifically targeting the performance of `document.getElementsByClassName` and `document.body.getElementsByClassName`. It assesses which approach can retrieve elements with a specific class name more efficiently.

### Benchmarks:

1. **`getElementsByClassName`**: 
   - **Code Example**: `const classElm = document.getElementsByClassName('aap')[0];`
   - **Description**: This function searches for elements with the class name 'aap' across the entire document.
   - **Execution Speed**: The latest benchmark results show that this approach has a performance of 8,804,723 executions per second.

2. **`body.getElementsByClassName`**:
   - **Code Example**: `const classElm = document.body.getElementsByClassName('aap')[0];`
   - **Description**: This function searches for elements with the class name 'aap', but only within the child nodes of the `<body>` element.
   - **Execution Speed**: The benchmark results indicate a performance of 7,221,052 executions per second for this method.

### Performance Comparison:

- **Pros of `document.getElementsByClassName`**:
  - This method searches the entire document, which may be beneficial if elements are not contained strictly within the body. 
  - Generally, it yields higher performance in this test case scenario.

- **Cons of `document.getElementsByClassName`**:
  - It may incur additional processing time if the DOM is large, as it scans more nodes.

- **Pros of `document.body.getElementsByClassName`**:
  - This method is potentially faster for documents where the relevant elements are guaranteed to be within the `<body>` tag since it limits its search to that part of the DOM.
  
- **Cons of `document.body.getElementsByClassName`**:
  - If you need to select elements that may reside outside of the body (e.g., in header or footer sections), this approach will miss them.

### Considerations:

- **DOM Structure**: The performance can vary depending on the complexity and size of the DOM. For very large pages, using `document.body.getElementsByClassName` might be preferable if it can be assured that all relevant elements are within the body.
  
- **Context Specificity**: If the code is reused across different HTML documents or requires generality, `document.getElementsByClassName` may be more suitable.

- **Browser Variability**: Testing was conducted in Chrome, and performance results might differ in other browsers due to differences in their JavaScript engines and DOM implementations.

### Alternatives:

- Other methods for selecting elements include `document.querySelector` and `document.querySelectorAll`, which allow for more complex selectors using CSS syntax. These methods are more versatile but may not perform as well as `getElementsByClassName` when dealing strictly with class names.

- Another alternative includes using third-party libraries like jQuery, which simplify element selection through a more consistent API but can add overhead to performance due to additional abstraction.

In summary, the benchmark highlights the performance differences between two similar DOM querying methods. For performance-critical applications, understanding the context in which these methods are used is essential for choosing the most appropriate one.

Related benchmarks:

document.body.getElementsByClassName vs document.getElementsByClassName + (version: 1)

Comparing performance of: getElementsByClassName vs body.getElementsByClassName

Created: one year ago by: Guest

Jump to the latest result

getElementsByClassName

body.getElementsByClassName

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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