Benchmark: getElementById().getElementsByClassName vs querySelectorAll

HTML Preparation code:

<div id="testdiv">
  <div id="unique">
    <span class="bueatiful">text</span>
    <span class="bueatiful">text</span>
    <span class="notBueatiful">text</span>
    <span class="bueatiful">text</span>
    <span class="bueatiful">text</span>
  </div>
</div>

Script Preparation code:

var i, imax;
var doc = document;

Tests:

getElementById().getElementsByClassName
var test = doc.getElementById('unique').getElementsByClassName('bueatiful');
querySelectorAll
var test = doc.querySelectorAll('#unique .beautiful')

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
getElementById().getElementsByClassName
querySelectorAll

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 3 years ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.124 Safari/537.36

Browser/OS: Chrome 91 on Windows

View result in a separate tab

Test name	Executions per second
getElementById().getElementsByClassName	8324149.0 Ops/sec
querySelectorAll	2505846.2 Ops/sec

Autogenerated LLM Summary (model llama3.2:3b, generated 2 months ago):

LLMs can make mistakes. Check important info.

Let's break down the provided benchmark definition and test cases.

**What is being tested?**

The benchmark measures the performance difference between two approaches for selecting elements in HTML:

1. `getElementById().getElementsByClassName`: This approach uses the `getElementById()` method to get a reference to an element with a given ID, and then calls the `getElementsByClassName()` method to retrieve all elements that match a specific class name.
2. `querySelectorAll`: This approach uses the `querySelectorAll()` method to select all elements that match a CSS selector.

**Options compared**

The benchmark compares two options:

1. Using `getElementsByName()` (not shown in the code snippet, but implied) vs using `getElementById().getElementsByClassName()`
2. Using `querySelectorAll` with different class names (`"beautiful"` and `"bueatiful"`)

**Pros and Cons of each approach**

1. **`getElementById().getElementsByClassName()`**
	* Pros:
		+ Can be more efficient if the element is guaranteed to exist and has a unique ID.
		+ Can be more reliable in older browsers that support this method.
	* Cons:
		+ Requires two separate calls to retrieve an element (one for `getElementById()` and one for `getElementsByClassName()`)
		+ May not return all matching elements if the element has multiple classes
2. **`querySelectorAll()`**
	* Pros:
		+ More concise and efficient, as it returns all matching elements in a single call.
		+ Can be more reliable with modern browsers that support this method.
	* Cons:
		+ May not work in older browsers or those that don't support the `querySelectorAll()` method
		+ Can return empty arrays if no matches are found

**Library usage**

In the test cases, the following library is used:

1. **Document Object Model (DOM)**: The `document` object and its methods (`getElementById()`, `getElementsByClassName()`, `querySelectorAll()`) are part of the DOM library.

**Special JavaScript feature or syntax**

None mentioned in this benchmark definition.

**Other considerations**

When choosing between these approaches, consider the following:

1. **Browser support**: Make sure to test your code on multiple browsers and versions that support `querySelectorAll()`.
2. **Performance**: Measure the execution time of each approach for different scenarios (e.g., number of matching elements).
3. **Readability and maintainability**: Choose an approach that is more concise, readable, and maintainable.

**Alternative approaches**

Other alternatives to consider:

1. **`querySelector` and `querySelectorAll()` with attribute selectors**: These methods can be used to select elements based on attributes (e.g., `[attr="value"]`).
2. **`querySelectorAll()` with pseudo-class selectors**: These methods can be used to select elements based on pseudo-classes (e.g., `:hover`, `:focus`).

Keep in mind that each approach has its own strengths and weaknesses, and the choice ultimately depends on the specific use case and requirements of your project.

Related benchmarks:

getElementById().getElementsByClassName vs querySelectorAll (version: 0)

Comparing performance of: getElementById().getElementsByClassName vs querySelectorAll

Created: 3 years ago by: Guest

Jump to the latest result

getElementById().getElementsByClassName

querySelectorAll

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 2 months ago):