Benchmark: getElementById vs getElementsByClassName[0]

HTML Preparation code:

<div id="testdiv">
  <div id="unique">testid</div>
  <div class="unique">testclass</div>
</div>

Tests:

getElementById
var byId = document.getElementById("#unique")
getElementsByClass[0]
var byClass = document.getElementsByClassName("unique")[0]

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
getElementById
getElementsByClass[0]

Fastest: N/A

Slowest: N/A

Latest run results:

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

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/92.0.4515.131 Safari/537.36

Browser/OS: Chrome 92 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
getElementById	5808419.0 Ops/sec
getElementsByClass[0]	4601559.5 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's dive into the benchmark and explain what's being tested.

**Benchmark Overview**

The benchmark compares two approaches to retrieving an HTML element:

1. `document.getElementById("unique")`
2. `document.getElementsByClassName("unique")[0]`

The benchmark aims to determine which approach is faster, more efficient, or both.

**Approach 1: `document.getElementById("unique")`**

This method uses a single method call to retrieve the first element with an ID of "unique". The method returns the matched element if found, or null if not.

Pros:

* Fast and efficient, as it only requires a single DOM lookup.
* Allows for easy filtering and iteration over matching elements.

Cons:

* May be slower than other methods if no match is found, leading to unnecessary DOM traversals.
* Limited flexibility, as it only returns the first matched element.

**Approach 2: `document.getElementsByClassName("unique")[0]`**

This method uses a single method call to retrieve the first element with a class of "unique". The method returns the matched element if found, or null if not.

Pros:

* Can be faster than `getElementById` for non-identical elements with the same class.
* More flexible than `getElementById`, as it can return multiple matching elements (although in this case, only one is retrieved).

Cons:

* May be slower than `getElementById` for identical elements with different IDs.
* Requires an additional step to filter out unwanted results.

**Library: `document`**

The `document` object represents the HTML document and provides a set of methods for interacting with its content. In this benchmark, the `document.getElementById` and `document.getElementsByClassName` methods are used to retrieve elements from the DOM.

**Special JS Feature/Syntax: None**

There is no special JavaScript feature or syntax being tested in this benchmark. Both approaches rely on standard JavaScript methods and do not involve any advanced features like async/await, promises, or generators.

**Other Alternatives**

If you're looking for alternative ways to retrieve elements from the DOM, consider:

* `document.querySelector`: A more modern approach that returns a single element or a list of elements matching the specified selector.
* `querySelectorAll`: Similar to `getElementsByClassName`, but allows for multiple matching elements and is supported by older browsers.

Keep in mind that these alternatives may have different performance characteristics, so it's essential to test them thoroughly to determine which one suits your use case best.

Related benchmarks:

getElementById vs getElementsByClassName[0] (version: 0)

Comparing performance of: getElementById vs getElementsByClass[0]

Created: 3 years ago by: Registered User

Jump to the latest result

getElementById

getElementsByClass[0]

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):