Benchmark: getElementById and getElementsByClassName[0] unique class

HTML Preparation code:

<div id="testdiv">
  <div id="unique1" class="unique" name="unique" data-unique="1">test1</div>
  <div id="unique2" class="unique1" name="unique" data-unique="2">test2</div>
  <div id="unique3" class="unique" name="unique" data-unique="3">test3</div>
  <div id="unique4" class="unique" name="unique" data-unique="4">test4</div>
  <div id="unique5" class="unique" name="unique" data-unique="5">test5</div>
</div>

Script Preparation code:

var i, imax;
var doc = document;

Tests:

getElementById
var test = doc.getElementById('testdiv').childNodes[0].innerHTML;
getElementById and getElementsByClassName
var test = doc.getElementsByClassName('unique1')[0].innerHTML;

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
getElementById
getElementById and getElementsByClassName

Fastest: N/A

Slowest: N/A

Latest run results:

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

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:136.0) Gecko/20100101 Firefox/136.0

Browser/OS: Firefox 136 on Windows

View result in a separate tab

Test name	Executions per second
getElementById	28853520.0 Ops/sec
getElementById and getElementsByClassName	21813820.0 Ops/sec

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

LLMs can make mistakes. Check important info.

The JSON provided represents a benchmark designed to compare the performance of two different methods for selecting a DOM element. Specifically, it tests:

1. **`getElementById`** method.
2. **`getElementsByClassName`** method.

### Benchmark Description

#### Options Compared:
1. **`getElementById('testdiv').childNodes[0].innerHTML`** 
   - This method retrieves the element with the ID `testdiv`, accesses its first child node, and reads its inner HTML.

2. **`getElementsByClassName('unique1')[0].innerHTML`**
   - This method retrieves the first DOM element with the class name `unique1` and reads its inner HTML.

### Pros and Cons of Different Approaches

**1. `getElementById`:**
   - **Pros:**
     - Fast: Generally, `getElementById` is faster than class-based selectors because it directly accesses an element by its ID, which is unique and indexed for quick access.
     - Simplicity: It's straightforward and clear for developers to use since an ID is guaranteed to be unique in a document.
   - **Cons:**
     - Limited Scope: It can only access one element at a time based on the ID, restricting its use when multiple similar elements must be queried.

**2. `getElementsByClassName`:**
   - **Pros:**
     - Multiple Elements: This method can select multiple elements at once if there are several elements with the same class name.
   - **Cons:**
     - Slower: It may be slower than `getElementById` due to its need to search for all elements with that class name, rather than directly accessing a single element by ID.
     - Returns a live HTMLCollection: The results can be updated automatically as the DOM changes, which may lead to unexpected behavior if the selected elements change after the selection.

### Other Considerations
- In terms of performance, the benchmark results show that `getElementById` has a higher number of executions per second (28,853,520) compared to `getElementsByClassName` (21,813,820). This confirms that retrieving elements by ID is typically more efficient for situations where a single element needs to be accessed.
  
### Alternative Approaches
In addition to the methods tested, there are other options that developers can use for DOM manipulation and querying:

1. **`querySelector`**: Allows selecting of elements using CSS selectors. For instance, `document.querySelector('#testdiv .unique1')` would return the first element with class `unique1` under the `testdiv`.
   - **Pros**: Very flexible due to CSS selector capabilities.
   - **Cons**: Slightly slower than `getElementById` and can be less predictable in performance depending on the complexity of the selectors.

2. **`querySelectorAll`**: Returns all matches of a CSS selector, giving a NodeList.
   - **Pros**: Can retrieve multiple elements using powerful selectors.
   - **Cons**: Similar performance drawbacks to `querySelector`.

3. **Using Libraries**: Libraries like jQuery provide abstraction over native DOM methods, offering convenience functions like `$('.unique1').html()` to achieve similar results. 
   - **Pros**: Simplifies and streamlines using DOM methods.
   - **Cons**: Introduces overhead in terms of file size and potential performance issues due to abstraction.

In conclusion, selecting the right method for DOM manipulation largely depends on the needs of the application, the expected frequency of access, and performance requirements. Each method has its trade-offs, and understanding them helps developers make informed choices based on the specific needs of their applications.

Related benchmarks:

getElementById and getElementsByClassName[0] unique class (version: 1)

Test performance of different ways of get just one particular DOM element

Comparing performance of: getElementById vs getElementById and getElementsByClassName

Created: one month ago by: Guest

Jump to the latest result

getElementById

getElementById and getElementsByClassName

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

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