Benchmark: getElementById vs getElementsByClassName a

HTML Preparation code:

<div id="a" class="b"></div>

Tests:

getElementById
document.getElementById('a'); a.innerHTML="abc";
getElementsByClassName
let b = document.getElementsByClassName('b')[0]; b.innerHTML="def";
querySelector
let c =document.querySelector(".b"); c.innerHTML="ghi";

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
getElementById
getElementsByClassName
querySelector

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 2 years ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36

Browser/OS: Chrome 120 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
getElementById	256072.3 Ops/sec
getElementsByClassName	322921.0 Ops/sec
querySelector	327859.8 Ops/sec

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

LLMs can make mistakes. Check important info.

**What is being tested?**

The provided benchmark measures the performance of three different ways to retrieve and manipulate an HTML element: `getElementById`, `getElementsByClassName`, and `querySelector`. The test case specifically targets the retrieval and manipulation of an element with the class name "b".

**Options compared**

1. **`document.getElementById('a')`**: This method retrieves the first element with the id "a". It's a simple and straightforward approach, but it might not be efficient if there are multiple elements with the same id.
2. **`let b = document.getElementsByClassName('b')[0];`**: This method retrieves all elements with the class name "b" and returns an array containing the first element. If no elements match, it returns an empty array. It's a bit more complex than `getElementById`, but it can be less efficient if there are many matching elements.
3. **`let c = document.querySelector('.b');`**: This method retrieves the first element that matches the CSS selector ".b". It's similar to `getElementsByClassName`, but it's generally faster and more flexible, as it allows for more complex selectors.

**Pros and Cons of each approach**

1. **`document.getElementById('a')`**:
	* Pros: Simple, fast, and efficient when there's only one matching element.
	* Cons: May be slow if there are multiple elements with the same id.
2. **`let b = document.getElementsByClassName('b')[0];`**:
	* Pros: More flexible than `getElementById`, as it can match multiple elements with the same class name.
	* Cons: Can be slower than `querySelector` when matching many elements, and it returns an array even if only one element matches.
3. **`let c = document.querySelector('.b');`**:
	* Pros: Fast and efficient, especially for complex selectors. Returns a single value (the first matched element) instead of an array.
	* Cons: May not be as flexible as `getElementsByClassName`, as it requires a more specific CSS selector.

**Library and its purpose**

None mentioned in the provided benchmark data.

**Special JS feature or syntax**

The test case uses JavaScript methods to retrieve and manipulate HTML elements, which is the standard way of interacting with DOM (Document Object Model) in JavaScript. No special features or syntax are used here.

**Other alternatives**

If you wanted to include other approaches, some alternatives could be:

1. **`document.querySelector('[class="b"]')`**: This method uses a different CSS selector that targets elements with the class name "b".
2. **`element.matches('.b')`**: This method checks if an element matches the CSS selector ".b" using the `matches()` method.
3. **`Array.prototype.find()`:** This method finds the first matching element in an array of elements that match a certain condition.

Note that these alternatives might not be included in the original benchmark, and their performance would depend on the specific use case and environment.

Related benchmarks:

getElementById vs getElementsByClassName a (version: 1)

a

Comparing performance of: getElementById vs getElementsByClassName vs querySelector

Created: 2 years ago by: Registered User

Jump to the latest result

getElementById

getElementsByClassName

querySelector

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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